Q20 of 805 Page 169

Helium atom has 2 electrons in its valence shell but its valency is not 2, Explain.

Helium’s valency is not 2 and is zero because the first shell can accommodate 2 electrons and in helium that shell is completely filled and no more electrons are left.


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18

Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them.

(a) Ammonia


(b) Carbon monoxide


(c) Hydrogen chloride


(d) Aluminum fluoride

 19

Write the molecular formulae for the following compounds

(a) Aluminum (III) nitrate


(b) Calcium (II) phosphate


(c) Mercury (II) chloride


(d) Magnesium (II) acetate

 21

If a person takes concentrated solution of salt. After sometime, he starts vomiting. What is the phenomenon responsible for such situation? Explain.

 22

Differentiate the following activities on the basis of voluntary or involuntary muscles.

(a) Jumping of frog


(b) Pumping of the heart


(c) Writing with hand


(d) Movement of chocolate in your intestine