Write balanced chemical equations for the following :
(i) Sodium nitrite is produced by absorbing the oxides of nitrogen in aqueous solution of washing soda.
(ii) Nitrogen is obtained in the reaction of aqueous ammonia with potassium permanganate.
(iii) Elemental phosphorus reacts with `conc. HNO_3` to give phosphoric acid.

Explanation

(i) `Na_2 CO_3 + NO + NO_2 rarr 2 NaNO_2 + CO_2`
(ii) `2 KMnO_4 + 2NH_3 rarr 2MnO_2 + 2KOH + N_2 + 2H_2 O`
`[MnO_4^(Ө) rarr MnO_2 , NH_3 rarr N_2]`
(iii) `P_4 + 20 NH_3 rarr 4H_3 PO_4 + 20 NO_2 + 4H_2 O`
`[P_4 rarr PO_4^(3 -) , NO_3^(Ө) rarr NO_2]`.