Q] Choose one option for each and explain how it is correct.
1) In bright sun in desert or on tar road presence of water is visualized. Why?
a) It is due to the refraction of light through different layers of air.
b) It is due to total internal reflection of light.
c) The reflection of light from the surface of water.
d) Irregular reflections.

2) What happens when excess of carbon dioxide is passed through clear lime water?
a) The liquid remains clean.
b) The liquid becomes cloudy.
c) Calcium carbonate is precipitated.
d) Calcium carbonate is first precipitated and then soluble calcium bicarbonate is formed.

3) Which of the following reaction is not a chemical change?
a) Burning of wood b) Melting of wax
c) Digestion of food d) Formation of A.T.P.

4) An element having atoms which have the same number of protons but different number of neutrons then what is that property?
a) Allotropy b) Isomerism c) Isotopic d) Variable valency

5) What will be the number of moles of oxygen molecules in 64 g of oxygen? Explain how?
a) 1 b) 2 c) 3 d) 4

2

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2014-09-05T11:30:54+05:30

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1 due to total internal reflection of light. the air close to ground is hotter and lighter. The density increases as the height increases temperature decreases.  Refractive index increases as height increases. Light from a tree top, from a height tries to enter lower layers of air with a large angle of incidence. more than the critical angle in the colder air. So it gets reflected totally

2 first calcium carbonate milky - insoluble - is formed - with excess co2 , calcium bicarbonate is formed - it is soluble - so milky solution becomes clear again

3 melting
4 isotopic
5 molecular weight of o2 = 32  as atomic number is 8 in one atom. atomic weight is 16. number of moles in 64g is 64/32

3 3 3
2014-09-05T11:46:07+05:30