(i) State any one reason for discarding 'Law of Octaves'.

(ii) What is periodicity? Explain the cause of periodicity.

How is the lightest gas collected and dried during its laboratory preparation?

Draw the shell diagram to explain the bond formation between an alkali metal and the halogen of the third period.

Explain the following assertions:

(i) Composition of dissolved air in water is different from ordinary air.

(ii) Steam at 100°C burns more severely than water at 100°C.

(iii) It is necessary to compare gases at STP.