Friday, September 23, 2011

CBSE Assessment of Practical Skills in Science class X

Set-1Practical Skills in Science
1. The two colours seen at the extreme ends of the pH chart are
(a) red and blue.  (b) red and green. (c) green and blue. (d) orange and green
Ans: (a) Red colour is at the top and blue colour is at the bottom.
2. A student observed that the colour of pH paper changes to green when shedipped it in water. She added a few drops of concentrated hydrochloric acid to the water. The colour of pH paper would turn to
(a) light red.  (b) apple green. (c) dark blue. (d) lemon yellow.
Ans: (a) The colour of pH paper is green in neutral medium, whereas it is red in acidic medium.
3. When zinc reacts with dilute hydrochloric acid
(a) the surface of zinc becomes brighter.   (b) the surface of zinc becomes black and dull.
(c) the metal turns into powder.                  (d) the reaction mixture turns green.
Ans: (b)  The surface becomes black and dull as the reaction proceeds
4. Students A, B and C were given five raisins each of equal weight. The raisins  were soaked in distilled water at room temperature. A removed the raisins after 20 minutes, B after two hours and C after 40 minutes. If PA, PB and PC denote percentage absorption of water obtained by students A, B and C respectively, then
(a) PA > PB > PC.    (b) PA < PB < PC. (c) PA < PB > PC. (d) PA = PB = PC.
Ans: 12 (c) Absorption of water increases with time up to its maximum limit.
5. A student dissolved 1 g of sugar in 10 mL of distilled water in a beaker A. He dissolved 10 g of sugar in 100 mL of distilled water in beaker B. Then he dropped a few raisins, in each. After two hours he found the raisins
(a) swollen in A and shrunken in B.  (b) shrunken in A and swollen in B.
(c) swollen in both.                            (d) shrunken in both.
Ans: (c)  Solutions in both A and B are hypotonic to raisins and hence they swell.
6. 10 mL of freshly prepared iron sulphate was taken in each of four test tubes. Strips of copper, iron, zinc and aluminium were introduced, each metal in a different test tube. A black residue was obtained in two of them. The right pair of metals forming the precipitates is
(a) copper and zinc. (b) aluminium and copper. (c) iron and aluminium. (d) zinc and aluminium.
Ans: (d)  Zinc and aluminium being more reactive will replace iron from iron sulphate.
7. A strip of copper was placed in a beaker containing zinc sulphate solution. On observing the strip the next day, it was noticed that
(a) the copper strip remained as it was.  (b) the copper strip became thinner.
(c) the copper strip became thicker.       (d) the colour of the strip changed.
An: (a)  Copper is less reactive than zinc and, therefore, no reaction occurs.
8. A student tested the pH of distilled water and found that the colour of the pH paper changed to green. He checked the pH again after dissolving a pinch of common salt in it. The colour of the pH paper this time was
(a) green. (b) yellow. (c) red. (d) blue.
Ans: (a) The pH paper in neutral medium gives green colour
9. Bottle A contains oxalic acid and bottle B contains sodium carbonate solution. When pH paper is dipped in each of the solutions, the colour seen in A and B respectively be
(a) orange, blue. (b) blue, orange. (c) green, blue.(d) orange, green.
Ans: (a) The colour of pH paper is orange in acidic medium while it is blue in basic medium.
10. The zinc metal used in the laboratory for doing experiments is available in the form of
(a) filings.  (b) strips.  (c) granules. (d) pellets
Ans:(c)  Zinc is available in the form of granules in the laboratory
11. When you place an iron strip in the solution of copper sulphate, the time required for the colour of the solution to change from blue to green is about
(a) a second. (b) an hour. (c) 8 hours.(d) 24 hours.
Ans: (b)  Metal deposition is not very fast and takes some time.
12. On adding sodium bicarbonate to acetic acid, you immediately
(a) observe strong effervescence.                                     (b) hear hissing sound.
 (c) get pungent smell.                                                     (d) notice formation of bubbles.
Ans: (a) The reaction between acetic acid and sodium bicarbonate to produce carbon dioxide is very fast.
13. A student sets up the apparatus for the experiment to show that CO2 is released during respiration. After 2 hours, he would observe
(a) KOH turning milky.                           (b) water level rising in the bent tube in the beaker.
(c) water level decreasing in the bent tube in the beaker.(d) water turning turbid in the beaker.
Ans: (b) CO2 released is absorbed by KOH. To fill the partial vacuum created in the conical flask, water rises in the bent tube.
 14. When you place an iron in copper sulphate solution, the reddish brown coating formed on the mail is       
(a) soft and dull.         (b) hard and flaky.      (c) smooth and shining.  (d) rough and granular.
Ans: (a) The freshly deposited copper is soft and dull.
15. In an experiment, to find the equivalent resistance of a series of combination of two resistors R1 and R2 student uses the ciruit shown here.
The circuit will give
(a) correct reading for volage V, but incorrect reading for current I.
(b) correct reading for current I, but incorrect reading for voltage V.
(c) correct reading for both current I and voltage V.
(d) incorrect readings for both current I and voltage V.
Ans:(b) The voltmeter has to be put in parallel with the resistances being measured and not across the ammeter.
1. A student dropped some pieces of marble in dilute HCl in a test tube. The gas evolved was passed through limewater. What change would be observed in limewater? 

(a) Becomes colourless (b) Changes to milky white (c) Changes to black (d) No significant change

2. What change takes place when zinc is treated with dilute nitric sulphuric acid? 

(a) Hydrogen is evolved (b) Nitrogen is evolved (c) Nitrogen dioxide is evolved (d) No Ammonia gas is released

3. What change takes place when sulphuric acid is added to a test tube containing water? 

(a) Test tube becomes cold (b) Test tube becomes hot (c) No significant change in temperature (d) A pungent gas is released

4. An aqueous solution of a salt turns red litmus blue. What would be the pH of that salt? 

(a) 4 (b) 2 (c) 7 (d) 13

5. Blue copper sulphate solution is added to a test tube containing zinc granules. What will be the colour of the resulting solution? 

(a) White (b) Blue (c) Green (d) Black

6. According to ohms law 

(a) R=V/I (b) R=1/V (c)V=R/I (d) I=VR

7. Which of the following is a non-ohmic conductor? 

(a) Copper (b) Aluminium (c) Silicon (d) Iron

8. Which of the following physical quantities of a conductor should be maintained in order to satisfy Ohm's law? 

(a) Length (b) Area of cross-section (c) Temperature (d) Colour

9. The commercial unit of electrical energy is: 

(a) Volt (b) Watt (c) Watt-hour (d) Kilowatt-hour

10. In an experiment related to electricity, which of the following is false? 

(a) An ammeter is always connected in series (b) A voltmeter is always connected in parallel 
(c) The positive terminal of a battery is always connected to the positive terminal of the ammeter in the circuit
(d) The negative terminal of a battery can be connected to the positive terminal of a voltmeter

11. In which of the following groups of organisms is food material broken down outside the body and then absorbed? 

(a) Euglena, Hibiscus, Drosera (b) Yeast, Mucor, Aspergillus (c) Man, Dog, Elephant (d) Lice, Mosquito, Bed bug

12. The reserve cellular energies in autotrophs and heterotrophs respectively are: 

(a) Starch and glycogen (b) Glycogen and starch (c) Proteins and fats (d) Carbohydrates and proteins

13. In which of the following groups is single circuit circulation seen? 

(a) Dog, Cat, Buffalo                             (b) Monkey, Apes, Lion 
(c) Catla catla, Exocoetus, Scoliodon   (d) Crocodile, Najanaja, Gallus gallus

14. Which of the following is not produced in the respiration of yeast? 

(a) Adenosine Tri Phosphate (b) Ethyl alcohol (c) Carbon dioxide (d) Water

15. Oxygenated blood is sent to the heart muscles through the:

(a) Brachial artery (b) Pulmonary artery (c) Coronary artery (d) Femoral artery

16. The phloem in plants is responsible for the transport of:

(a) Sugars (b) Water and mineral salts (c) Sugars, water and mineral salts (d) Chitin

1. (b) 2. (a) 3. (b) 4. (d) 5. (a) 6. (a) 7. (c) 8. (c) 9. (d) 10. (d) 11. (b) 12. (a) 13. (c) 14. (d) 15. (c) 16. (a)

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