(a) Draw the structures of the following :
(i) `XeF_(4)`
(ii) `H_(2)S_(2)O_(7)`
(iii) `SO_(3)^(2-)`
(b) Explain the following observations :
(i) Phosphorous has a greater tendency for catenation than nitrogen.
(ii) The negative value of electron gain enthalpy is less for fluorine than that for chlorine.
(iii) Hydrogen fluoride has a much higher boiling point than hydrogen chloride.

Explanation

(a) (i) see Q. 11 (i) , Set I, Delhi Board, 2009.
(ii) See Q. 29 (a) (i) (or part), Outside Delhi , 2009 .
(b) (i) The property Catenation depends upon the strength of the element - element bond since p-p (213 kJ mol^9-1)` bond strength is much more than N-N bond strength .So phosphorus has greater tendency for catenation than nitrogen.
(ii) The electron gain enthalpy of flurine is less negative than that of chlorine due to the small size of flurine atom.
(iii) Hydrogen fluoride has a much higher boiling point (b.p .293 K ) due to strong hydrogen bonding.