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Sunday, November 4, 2018

CBSE/NCERT Board Solved Questions class X NCERT Ch. Periodic Classification

 Solved Questions Set-01
Q.1. Why does silicon is classified as Metalloid?

Ans: Silicon is gray color solid at room temperature with very high melting point and boiling point that lose or gain 4 electrons 3s2, 3p2] having both metallic and non metallic properties so it is classified as Metalloid eg. Sio2
Q.2.Why inert gases have zero valencies?

Ans: It is because Inert gases have 2 or 8 electrons in valence shell.

Q.3. How is valency of an element determined?

Ans: The valency of an element measures its ability to combine with other elements. The valency is determined by knowing place in periodic table.. All the elements in group VIII have eight electrons in their outer shells, and thus have a valency of zero (highly stable). Elements in group I just have one valence electron in their outer shells and thus have a valency of one.

Q.4. why could no fixed position be given to hydrogen in Mendeleev’s Periodic table?

Ans: Hydrogen placed in the first column above alkali metals. it is because hydrogen and alkali metals have similar properties.
However, hydrogen also resembles halogens. Like halogens, hydrogen is a gas, and exists as a diatomic molecule (H2). It forms covalent compounds like halogens unlike alkali metals. Hence, it can also be placed above the halogen group .Therefore, Mendeleev was not able to explain the position of hydrogen.

Q.5. In modern periodic table, the isotopes of Chlorine Cl-35 and Cl-37 having different atomic masses will 
be kept in different slots or they would be assigned same position on the basis of their chemical properties? Give reason in support of your answer

Ans: It is because periodic table is based on the atomic numbers of the element and both the isotopes of chlorine have the same atomic number (Z = 17).

Q.6. Why was Dobereiner’s system of classification of elements into triads not found to be useful?

Ans: it is because he could not arrange all elements in triads.

Q.7. Oxygen (O, 8) and sulphur (S, 16) belong to group 16 of the periodic table :-
(i) Write the electronic configuration and valency of these two elements?
(ii) Which among these will be more electronegative? Why?

Ans: (i) Oxygen (O, 8) = 2,6  ; Vacancy =2           Sulphur (S, 16) = 2,8,6 ; Vacancy =2  
(ii) Oxygen will be more electronegative due to electro negativity decreases from top to bottom because atomic size increases.

Q.8. How does electronic configuration of atoms change in a period with increase in atomic number?

Ans. On moving across a period from left to right, the atomic number of the elements increases, therefore, the number of electrons in the valence shell increases from 1 to 8, i.e, the first element in the given period will have one electron in its valence shell and the last element in the same period will have eight electrons.

Q.9. What happens to the melting points and boiling points of elements while moving down in a group?

Ans. The melting points and boiling points decrease while moving down in group of metals.
The melting points and boiling points increases while moving down in group of non-metals.

Q10. Why Chlorine (atomic number 17) is more electronegative than sulphur (atomic number 16)

Ans: The nucleus of chlorine has more tendency to attract an extra electron than the nucleus of sulphur because chlorine needs only one 1 electron to complete its shell. Hence, chlorine is more electronegative than sulphur.

 Solved Questions Set-02

1. How does the electronic configuration of an atom relate to its position in the Modern periodic table?

Ans. The outermost electron in  electronic configuration give idea of group in Modern periodic table and also period.

2. Give examples of some :  a. Metalloids b. Alkali metals c. Halogens d. Alkaline Earth metals e. Nobel gases or inert elements

Ans: a. Metalloids – Boron, Silicon, Germanium
b. Alkali metals – Sodium, lithium, Potassium
c. Halogens – Fluorine, Chlorine, Bromine
d. Alkaline Earth metals – Magnesium, Calcium
e. Nobel gases or inert elements – Helium, Neon, Krypton

3. How were the positions of different isotopes decided in modern periodic table? 

Ans: All the isotopes of an element have same atomic numbers. In modern periodic table, the elements have been allotted places based on their atomic numbers. Therefore, all the isotopes of an element have been assigned the same position in the modern periodic table

4. Where do you think hydrogen should be placed in the modern periodic table?

Ans: The modern periodic table is based on the atomic numbers of the elements and also upon their electronic distribution. Alkali metals as well as hydrogen have one electron in their valence shell. Therefore, hydrogen should be placed in the group of alkali metals. However, it has been assigned a separate position and is not a member of the group of alkali metals since it is a non-metal.

5. How were the positions of the elements Co and Ni resolved in the modern periodic table?

Ans: On the basis of atomic masses, Ni (58.7) should be placed before Co (58.9). This was defect in Mendeleev’s table because the element Co was placed before Ni. However, the atomic number of (Co = 27) is less than that of Ni ( 28). Therefore, they have been correctly arranged in the modern periodic table.

6. The two isotopes of chlorine have atomic masses 35 u and 37 u. Should they be placed in same slot in the periodic table?

Ans: Yes, they should be placed in the same slot because periodic table is based on the atomic numbers of the element and both the isotopes of chlorine have the same atomic number (Z = 17).

7. Which element is bigger in size, lithium (Z = 3) or Sodium (Z = 11) and why?

Ans: Lithium (Li) atom has only two shells K and L in it whereas a sodium (Na) atom has three shells K L and M. Since a sodium atom has one mote shell than a lithium atom, therefore sodium atom is bigger in size.

8. What were the criteria used by Mendeleev in creating his periodic table?

Ans: Ans. Mendeleev’s periodic table was based on the observation that properties of the elements are a periodic function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then elements with similar properties get their place in the same group in a successive increasing order of atomic masses.

9. Why did Mendeleev leave some gaps in his periodic table?

Ans. Mendeleev left gaps in his periodic table to keep the elements with similar properties together if predicted. New elements would be discovered later and they would occupy those gaps.

10. Why did Mendeleev treated the hydrides and oxides of element as the basic properties  of elements for their classification?

Ans. During the period when Mendeleev gave his periodic table atomic numbers and electronic configurations were not known. Comparison of properties of elements could be best done by comparing their compounds. He selected oxides and hydrides because oxygen and hydrogen form compounds with most of the elements due to their high reactivity.

11. Why are the elements in the same group of the periodic table show close resemblance in their chemical behavior?

Ans: The chemical properties depend upon the number of valence electrons of an element. The elements in the same group of the periodic table show close resemblance in their chemical behavior as they have same number of valence electrons.

12. What happens to atomic radii in a group and period and why?

Ans: Atomic radius is the distance between the centre of atom and the outermost shell.

In a period, atomic radius generally decreases from left to right.

In a period there is a gradual increase in the nuclear charge. Since valence electrons are added in the same   shell, they are more and more strongly attracted towards nucleus. This gradually decreases atomic radii.

Atomic radii increase in a group from top to bottom.

As we go down a group the number of shells increases and valence electrons are present in higher shell and the distance of valence electrons from nucleus increases. Also, the number of filled shells between valence electrons and nucleus increases Both the factors decrease the force of attraction between nucleus and valence electron. Therefore, atomic size increases on moving down a group.

13. Why are the ionization energy of elements increases in a period from left to right.

Ans: The minimum amount of energy required to remove an electron from a gaseous atom in its ground state to form a gaseous ion is called ionization energy.
The ionization energy increases in a period from left to right. This is because the force of attraction between valence electron and nucleus increases in a period from left to right.

14. What do you mean by Electron affinity: How it is vary in group and periods in modern periodic table?

Ans: The tendency of element to gain an additional electron. This ability is measured by electron affinity. It is the energy change when an electron is accepted by an atom in the gaseous state. Electron affinity is assigned a positive value when energy is released during the process. Greater the value of electron affinity, more energy is released during the process and greater is the tendency of the atom to gain electron.
In a group, the electron affinity decreases on moving from top to bottom as less and less amount of energy is released.
In a period, the electron affinity increases from left to right, as more and more amount of energy is released

15. What do you mean by Electro negativity?

Ans: Electro negativity is relative tendency of a bonded atom to attract the bond-electrons towards itself. It just compares the tendency of various elements to attract the bond-electrons towards themselves.
Electro negativity decreases in a group from top to bottom. Electro negativity increases in a period from left to right. Electro negativity is related to ionization energy. Electrons with low ionization energies have low electro negativity because their nuclei do not exert a strong attractive force on electrons. Elements with high ionization energies have high electro negativity due to the strong pull exerted on electrons by the nucleus.

Solved Questions Set-03

VERY SHORT ANSWER TYPE QUESTION (1 MARKS)

1. In the modern periodic table which are the metals among the first ten elements.

Ans. Only lithium, beryllium.

2. By considering their position in the periodic table which one of the following elements would you expect to have maximum metallic characteristic? Ga, Ge, As, Se, Be.

Ans. Ga.

3. Which of the following statement is not correct statement about the trends when going from left to right across the periods of periodic table.
A. The element becomes less metallic in nature.
B. The number of valence electron increase.
C. The atoms lose their electron more easily
D. The oxide becomes more acidic

Ans. The atoms lose their electron more easily.

4. Element X forms a chloride with the formula XCl2 which is solid with a high melting point. X would most likely be in the same group of periodic table as (a). Na (b). Mg (c). Al  (d). Si?

Ans. (b). Mg

5. Which element has two shells, both of which are completely filled with electrons?

Ans. Ne (2,8).

6. The electronic configuration 2, 8, 2 ?

Ans. Mg (2,8,2).

7. A total of three shells, with four electrons in its valence shell?

Ans. Si (2,8,4).

8. A total of three shells, with three electron in its valence shell?

Ans. Al(2,8,3).

9. Twice as many electrons in its second shell as in its first shell?

Ans. C (2,4).

10. Nitrogen(atomic number=7) and phosphorus(atomic number=15) belong to same group-15 of the periodic table. Write the electronic configuration of these two elements. Which of these two will be more electronegative? Why.

Ans. Electronic configuration of N (7) = 2, 5 Electronic configuration of P (15) = 2, 8,5 
Nitrogen will be more electronegative due to electro negativity decreases from top to bottom because atomic size increases.

11. In the modern periodic table Ca (At no. = 20) is surrounded by elements with atomic number 12, 19, 21, and 38. Which of these have physical and chemical properties resembling Ca.

Ans. 38,12

VERY SHORT ANSWER TYPE QUESTION (2-marks each)

Q.1. Did Doberenier‘s triads also exist in the column of Newland octaves. Compare and find out.

Ans. Yes, Li, Na, K

Q.2. What are the limitation of Dobernier‘s classification?

Ans. Only few elements are classified into triads. So, this classification is rejected.

Q.3. What are the limitations of Newlands law of Octaves

Ans. (a) It was applicable only upto atomic mass 40 of Ca. (b) Two elements Ni and Co are placed in column as F, Cl, Br which have different properties.

Q.4. Use Mendeleev‘s periodic table to predict the formula for the oxide of following element K, C, Ba, Al

Ans. K –I A –K2O C -IV A –CO2 Al –III A-Al2O3 Ba –II A –BaO

Q.5.Besides Ga, which other elements have been discovered that were left by Mendeleev in his periodic table (Any two)?

Ans. Eka-Boron-Scandium Eka-Silicon-Germanium

Q.6. What were the criteria used by Mendeleev in creating his periodic table?

Ans. Two criteria used by Mendeleev (i) Atomic mass   (ii) Similar chemical properties

Q.7. Why do you think the noble gases are placed in a separate group?

 Ans. These gases were discovered very late and placed in a separate group because they were inert.

Q.8. Name two elements you would expect to show chemical reaction, similar to magnesium. What is the  basis for your choice?

Ans. Ca, Be On the basis of the elements belong to same group-2. So valance electrons are same.

Q.9. (a) What property do all elements in the same column of the periodic table as Boron have in common
        b) What property do all elements in the same column of the periodic table as Fluorine have in common?

Ans. (a)  All elements in the same column as Boron have 3e- in valence shell and form oxide X2O3.
       (b)  All elements in the same column as Fluorine have 7e- in valence shell so their valency is one.

Q.10. An atom has electronic configuration 2,8,7 (a) What is the atomic no. of this element? (b) To which of the following elements would it be chemically similar N(7) F(9) P(15) Ar(18)

Ans. (a) Atomic no=17 (b) F(9).

Short answer type question (3-marks each)

Q.1-How could the modern periodic table remove various anomalies of Mendeleev’s periodic table?

Ans-Various anomalies are removed in following ways-

(a) The position for all isotopes of an element justified since they have same atomic number.
(b) The position of certain elements which are earlier misfit like Co-58.9 is placed before Ni-58.7 are now justified because Co has lower atomic number than Ni.
(c) Cause of periodicity explained due to same electronic configuration repeated after certain gap.

Q.2- Name
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shell.

Ans- (a) Li ,Na ,K(Group-1)
        (b Be ,Mg (Group-2) 
       (3) Ne ,Ar, Kr (Group-18)

Q.3- (a) Li,Na,K are all metals that react with water to liberate H2 gas .Is there any similarity in the atoms of these elements.
(b) Helium is an unreactive gas and Neon gas is a gas of extremely low reactivity, what do their atoms have in common.

Ans-(a) there are following similarities.
(1) these atoms have same number of electrons in outermost shell   3Li -2,1 11Na-2,8,1 19K-2,8,8,1
(2) Li,Na,K react with oxygen to form oxide which are basic in nature.  
(b) both He and Ne have completely filled shell

Q.4-The position of three elements A,B and C in the periodic table are shown below

Group-16
Group-17
           -
-
          -
A
          -
-
          B
C
 (a) State whether A is a metal or non-metals. 
 (b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size then B.       
(d) Which type of ion, cat ion or anion will be formed by element A

Ans-(a)-Non-metal
(b) A is more reactive due to small size, have more tendency to accept outside electron
(c) C is smaller in size than B due to atomic size decreases from left to right in a period
(d) Anion formed due to tendency to accept electron

Q5. How are the positions of elements related to their atomic number in the Modern periodic table?

Ans. The number of valence electrons present in an atom of an element is equivalent to  the group number, while the total number of shells give the period number in which the element to present.
e.g.  1. Atomic no. of Mg=12 ;  Electronic configuration=2,8,2     therefore, Group. no.=2 or IIA   Period no.=3 e.g. 2. Atomic no. of Cl=17; Electronic Configuration=2,8,7       therefore, Groupp. no.=17th  or VIIA

Solved Questions Set-04

Q1. What is Modern periodic Law?

Ans. The Properties of elements are a periodic function of their atomic number.

Q2. What were the limitations of Dobereiner Law of triads?

Ans. Dobereiner could identify only 3 triads from the element known at that time. Hence, this system is not useful.

Q3. State Newlands’s law of Octaves.

Ans. Newland arranged the elements in the increasing order of the atomic masses and found that every eight element had properties similar to that of the first like the notes of music.

Q4. What were the limitations of Newlands’s Law of Octaves?

Ans. 1. It was only applicable only up to Calcium as after Calcium every eighth element did  not posses , properties similar to that of first.

2. At a few places unlike elements were put together like cobalt and nickel along with F, Cl and Br.

Q5. Which 2 criteria did Mendeleev used to classify elements in his periodic table?

Ans. Atomic mass and similarity in chemical property.

Q6. State Mendeleev’s periodic law.

Ans. Properties of elements are a periodic function of their atomic masses.

Q7. Why did Mendeleev leave gap in his periodic table?

Ans. Mendeleev place elements with similar properties one below the other leaving gap  for yet undiscovered elements.

Q8. Name the elements which have since been discovered that were left by Mendeleev  in his Periodic Table?
Ans. Eka Boron – Scandium             Eka   Al - Gallium         Eka   Si - Germanium

Q9. What are the limitations of Mendeleev's periodic table?
Ans.
1. Position of Isotopes was not clear in his table.
2. Wrong Order of atomic mass of certain elements  – Elements with higher atomic  mass were placed before elements having lower atomic mass.    e.g. Cobalt was placed before nickel.
3. Position of hydrogen was not clear in his periodic table.

Q10. How were the drawbacks of Mendeleev's periodic table resolved in the modern periodic table?

Ans.  As the modern periodic table was based on the atomic numbers so all the isotopes could be placed together in one slot.  Secondly, the wrong order of atomic masses was also sorted as Cobalt's atomic number was lower than Nickel even though it had a higher atomic mass.

Links For CBSE Class X Science Term-II

CBSE E-Notes-Heredity and evolution - X Biology


Class 10 Heredity and Evolution – Gist of lesson
Genetics : Branch of science that deals with Heredity and variation.
Heredity : It means the transmission of features / characters/ traits from one generation to the next generation.
Variation : The differences among the individuals of a species/population are called variations.
Mendel and His Work on Inheritance
Gregor Johann Mendel started his experiments on plant breeding and hybridization. He proposed the laws of inheritance in living organisms. Mendel was known as Father of Genetics
Plant selected by Mendel : Pisum sativum (garden pea). Mendel used a number of contrasting characters for garden pea.
Following are the seven pairs of contrasting characters in Garden Pea
(TABLE OF CONTRASTING CHARACTERS. SEVEN PARTS)
CHARACTER
DOMINANT TRAIT
RECESSIVE TRAIT
Flower colour
Violet
White
Flower position
Axial
Terminal
Seed colour
Yellow
Green
Seed shape
Round
Wrinkled
Pod shape
Inflated
Constricted
Pod colour
Green
Yellow
Height of plant   
Tall
Dwarf/Short

Mendels Experiments : Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time)

Monohybrid Cross : Cross between two pea plants with one pair of contrasting characters is called a monohybrid cross. Example : Cross between a tall and a draft plant (short).
Observations of Monohybrid Cross
1. All F1 progeny were tall (no medium height plant (half way characteristic)
2. F2 progeny ¼ were short, ¾ were tall
3. Phenotypic ratio F2 – 3:1 (3 tall : 1 short)
Genotypic ratio F2 – 1 : 2 :1  = TT : Tt : tt
Conclusions
1. TT and Tt both are tall plants while tt is a short plant.
2. A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.
3. Characters/Traits like 'T' are called dominant trait (because it express itself) and ‘t’ are recessive trait (because it remains suppressed)
Dihybrid Cross : A cross macle between two plants having two pairs of contrasting characters is called dihybrid cross.

PARENT GENERATION  ---> ROUND GREEN SEEDS x WRINKLED YELLOW SEEDS      
Phenotypic Ratio
Observations
1. When RRyy was crossed with rrYY in F1 generation all were Rr Yy round and yellow seeds.
2. Self pollination of F1 plants gave parental phenotype and two mixtures (recombinants round yellow & wrinkled green) seeds plants in the ratio of 9:3:3:1
Conclusions
1. Round and yellow seeds are DOMINANT characters
2. Occurrence of new phenotypic combinations show that genes for round and yellow seeds are inherited independently of each other
SEX DETERMINATION : Phenomenon of decision or determination of sex of an offspring
FACTORS Responsible for Sex Determination
1. Environmental : In some animals the temperature at which the fertilised eggs are kept decides the gender. eg. in Turtle                                                                                  2. Genetic : In some animals like humans gender or individual is determined by a pair of chromosome called sex chromosome  XX – Female and XY – Male
This shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless whether they are boys or girls. Thus sex of children will be determined by what they inherit from their father, and not from their mother.
EVOLUTION
Evaluation is the sequence of gradual changes which takes place in the primitive organisms, over millions of years, in which new species are produced.
Situation-I

Group of red beetles


Colour variation arises during reproduction

All beetles red except one that is green
One beetle Green Reproduction
Crows feed on red beetle
Progeny beetles green
No. of beetles reduces
Crow could not feed on green beetles as they got camouflaged in green bushes

Number of green beetles increases

Situation 1 : Green beetles got the survival advantage or they were naturally selected as they were not visible in green bushes. This natural selection is exerted by crows resulting in adaptations in the beetles to fit better in their environment  
Situation 2 : Blue beetles did not get survivals advantage. Elephant suddenly caused major havoc in beetle population otherwise their number would have been considerably large.
From this we can conclude that accidents can change the frequency of some genes even if they do not get survival advantage: This is called genetic drift and it leads to variation.
Characters or traits of an organism are controlled by the genes
A Section of DNA (cellular)

         Gene

   Provides information

  For synthesis of Proteins

 Proteins controls a character
Example :
Gene T
responsible for synthesis of efficient enzyme (Protein)
More production
of growth hormone

Results in Tall Plants

Gene t
responsible for synthesis of less  efficient enzyme


Less production
of growth hormone

Results in short Plants

Genetic drift. It leads to diversity without any adaptation
SITUATION-III
Group of red beetles
Habitat of beetles (bushes)
Suffer from plant disease
Average weight of beetles
decreases due to poor nourishment
Number of beetles kept on reducing
Later plant disease gets eliminated
Number and average weight of the beetles increases again

Situation 3 : No genetic change has occurred in the population of beetle. The population gets affected for a short duration only due to environmental changes.

ACQUIRED AND INHERITED TRAITS
Acquired Traits
Inherited Traits
1. These are the traits which are developed in an individual due to special conditions
1. These are the traits which are passed from one generation to the next.
2. They cannot be transferred to the progeny
2. They get transferred to the progeny.
3. They cannot direct evolution eg. Low weight of starving beetles.
3. They are helpful in evolution. eg. Colour of eyes and hair

SPECIATION
Micro evolution : It is the evolution which is on a small scale. eg. change in body colour of beetles.
The process by which new species develop from the existing species is known as speciation.
Speciation : it is the process of formation of new species. 
Species : A group of similar individuals within a population that can interbreed and produce fertile offspring.
Geneflow : It is exchange of genetic material by interbreeding between populations of same species or individuals
WAYS BY WHICH SPECIATION TAKES PLACE
Speciation takes place when variation is combined with geographical isolation.
Gene flow : occurs between population that are partly but not completely separated
GENETIC DRIFT
It is the random change in the frequency of alleles (gene pair) in a population over successive generations.
*Natural Selection : The process by which nature selects and consolidate those organisms which are more suitably adapted and possesses favorable variations 
Genetic drift takes place due to 
(a) Severe changes in the DNA  (b) Change in number of chromosomes
Evolution and classification
Both evolution and classification are interlinked.
1. Classification of species is reflection of their evolutionary relationship.
2. The more characteristic two species have in common the more closely they are related.
3. The more closely they are related, the more recently they have a common ancestor.

4. Similarities among organisms allow us to group them together and to study their characteristic.
TRACING EVOLUTIONARY RELATIONSHIPS
(Evidences of Evolution)
I. Homologous Organs : (Morphological and anatomical evidences. These are the organs that have same basic structural plan and origin but different functions.
Homologous organs provides evidence for evolution by telling us that they are derived from the same ancestor.
Example :
Forelimb of Horse
(Running)
Same basic structural but different functions perform.
Winds of bat
(flying) plan,
Paw of a cat
(walk/scratch/attack)
II. Analogous Organs : These are the organs that have different origin and structural plan but same function example :
Example : Analogous organs provide mechanism for evolution.
Wings of bat       elongated fingers with skin folds

Wings of bird     Feathery covering along the arm

Different basic structure, but perform similar function i.e., flight

III. Fossils : (Palaeontological evidences) : The remains and relics of dead organisms of the past.

FOSSILS ARE PRESERVED TRACES OF LIVING ORGANISMS
Fossil Archaeopteryx possess features of reptiles as well as birds. This suggests that birds have evolved from reptiles. Examples of Fossils

AMMONITE - Fossil-invertebrate                
TRILOBITE - Fossil-invertebrate
KNIGHTIA - Fossil-fish                                 
RAJASAURUS - Fossil dinosaur skull

AGE OF THE FOSSILS

I. Deeper the fossil, older it is.                                                                                                           
II. Detecting the ratios of difference of the same element in the fossil material i.e. Radio-carbon dating [C-(14) dating)
Evolution by stages : Evolution takes place in stages ie bit by bit over generations.
I. Fitness advantage
Evolution of Eyes
Evolution of complex organs is not sudden it occurs due to minor changes in DNA, however takes place bit by bit over generations.


Flat worm has rudimentary eyes
Insects have compound eyes                 enough to give fitness advantage
Humans have binocular eyes

II. Functional Advantage
Evolutions of feathers :
Feathers provide insulation in cold weather but later they might become useful for flight.
Example : Dinosaurs had feathers, but could not fly using feathers. Birds seem to have later adapted the feathers to flight.
Evolution by Artificial Selection :
Humans have been a powerful agent in modifying wild species to suit their own requirement throughout ages by using artificial selection. eg
(i) From wild cabbage many varieties like broccoli, cauliflower, red cabbage, kale, cabbage and kohlrabi were obtained by artificial selection.
(ii) Wheat (many varieties obtained due to artificial selection).
Molecular Phylogeny
Þ  It is based on the idea that changes in DNA during reproduction are the basic events in evolution

Þ Organisms which are more distantly related will accumulate greater differences in their DNA

                                         HUMAN EVOLUTION

Tools to Study Human Evolutionary Relationship
 
Excavating         Time dating        Fossils    Determining DNA Sequences

Although there is great diversity of human forms all over the world get all humans are a single species.

Chapter - 9: Heredity and Evolution
Assignment  for practice before  exam
CBSE Notes-Heredity & evolution
Point to remember- To revise before exam
NCERT Solutions Heredity & evolution
CBSE Notes-Heredity & evolution
Heredity and Evolution Questions for practice
Heredity and Evolution  Guess questions 
Heredity and Evolution  Notes
Heredity and Evolution[Solved Questions]-1
Heredity and Evolution[Solved Questions]-2
Heredity and Evolution[Solved Questions]-3