(A) Complete the following chemical equations :
(i) `Cu+HNO_(3)` (dilute) `to`
(ii) `XeF_(4)+O_(2)F_(2)to`
(B) Explain the following observations:
(i) Phosphorous has greater tendency for catenation than nitrogen.
(ii) Oxygen is a gas but sulphur is a solid.
(iii) The halogens are coloured. Why ?

Explanation

(a) `(i) 3Cu+8HNO_(3)` (dil.)`to 3Cu(NO_(3))_(2)(aq)+2NO(g)+4H_(2)O(I)`
(ii) `XeF_(4)+O_(2)F_(2) to XeF_(6) to XeF_(6)+O_(2)`
(b) It is because N-N bond is weaker than P-P bond due to more interelectronic repulsion due to smaller size.
(ii) Oxygen is diatomic therefore, having less van der Waal's forces of attraction whereas sulphur is octa-atomic, thus hs more van der Wall's forces of attraction.
(iii) They are coloured because their moleucles absorb light from visible and outer electrons get excited to higher energy level. When they come back to lower level. They radiates complementary colours.