CBSE ADDA

Chapter – 3 ATOMS AND MOLECULES  1.  An old man and a scientist were talking about a deserted house. The old man was sure that it was haunted by ghosts, but the scientist discarded the view saying no one had ever seen a ghost. The old man was annoyed and challenged the scientist about existence of atoms, sub-atomic particles which also could not be seen. · Name the three sub-atomic particles and their discoverers. · Whose viewpoint do you support and why? 2.  An activity was conducted in a classroom where students held placards with symbols and valency of the elements separately. Each student held two placards, one with the symbol in the right hand and other with the valency in the left hand. · Which placards will be required for formation of sodium chloride ( both symbol as well as valency). · Which qualities are required in the student to perform such a group activity? 3.  Two class IX students, Kaveri and Nalin, were asked to take 5.3 g of sodiu...

CBSE-CH: Floatation GRAVITATION]                              Q1.While passing nearby a pond, some students saw a drowning man screaming forhelp. They alerted another passerby, who immediately threw an inflated rubber tube in the pond. The man was saved.· Why the passerby did use inflated rubber tube to save the  drowning man? ·Write the principle involved here.· Which qualities shown by the students and the passerby do you identify that helped in saving the drowning man? Q2.You received  an e-mail from  a friend living in  a coastal town. He shared an experience with you that recently, while swimming on the coastline of the sea in common swimming attire, he thought of going deeper inside the sea. He was asked to abstain from delving deeper into the sea by the rescue personnel. Respond  to the following questions using the information provided above.Why the rescue personnel asked...

Q. Explain the process of waste water treatment? Ans: The wastewater is treated through physical, chemical, and biological processes to remove the physical, chemical and biological contaminants. Physical - separates the large waste Biological- Adding of microorganisms to digest waste and produce oxygen in water Chemical- Chlorine and other chemicals are added into the water to finally purify it. Q. what is sewage? Ans: Wastewater is generated during various activities in homes, industries, hospitals, offices, and laundry services etc. This waste water is called sewage. Q. Explain the vercomposting toilet ?            Ans: Vermicomposting toilets are those which do not use water and are very environment friendly. They can be utilized in areas where water is a scarcity and can also be used in forests and other areas where sewage lines have not been built. This process uses worms for decomposition of waste. The waste is degraded i...

2 Marks Questions [2 x 5 = 10 ] 1. An element has electronic  configuration  2, 8, 3. What is the atomic  number  of this element? To which (i) group and (ii) period this element belong? 2. State the positions of (i) isotopes of the same element and (ii) hydrogen in the Modern Periodic Table. 3. How does the tendency to gain electrons change as we go down the 16th group of periodic table? Why? 4. Give reasons for the following :  (a) Lithium atom is smaller than  sodium  atom. (b) Chlorine (atomicnumber 17) is more electronegative than sulphur (atomic number 16) 5. (a) State the Modern Periodic Law.  (b) Name the element which has twice as many electrons in its second shell as in its first shell. Write its electronic configuration also. 3 Marks Questions [ 3 x 5 = 15 ] 1. An element X belongs to group 17 and third period of the periodic table.  (a) Write electronicconfiguration of the e...

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