(a) Complete the followingh chemical reaction equations :
(i) `Cu+HNO_(3 (dilute))to`
(ii) `P_4+NaOH+H_2Oto`
(b) (i) why does `R_3P=O` exist but `R_3N=O` does not ? (R=alkyl group)
(ii) why is dioxygen a gas but sulphur a solid ?
(iii) why are halogens coloured ?

Explanation

(a) (i) `3Cu+8HNO_3("dilute") to 3Cu(NO3)_2+2NO+4H_2O`
(ii) `P_4+3NaOH+3H_2Oto Ph_3+3NaH_2PO_2`
(b) (i) N (unlike P ) lacks the d-orbital. This restricts nitrogen to expand its co-ordination number beyond four.
(ii) Oxygen exist as a diatomic molecule while sulphur exists as a polyatomic molecule hence sulphurs mass will be more therefore it will have more van der waal forces, hence more boiling point. Diatomic oxygen, will have boiling point therefore, it is present in gaseous state.
(iii) Halogens are coloured becasue they possess a valene shell electronic configuration `S^2,S^5`. This means that they contain unpaired electrons in their outer most p-orbital. these electorns absorb light and get promoted to higher orbitals.
When they returs to their ground state, they emit radiations which fall in the visible region of electromagnetic spectrum. Hence, they appear as coloured.