Explain why PAN is called a secondary pollutant.

The following reaction takes place in the car's catalytic converter once it is warmed up: 

$2\mathrm{CO}\left(\mathrm{g}\right) + 2\mathrm{NO}\left(\mathrm{g}\right) \to 2{\mathrm{CO}}_2\left(\mathrm{g}\right) +{\mathrm{N}}_2\left(\mathrm{g}\right)$

Use oxidation numbers to explain which species is reduced and which is oxidised in the reaction.

Ammonia is made from its elements in the Haber process. For the ammonium ion give formula.

(A) ${{\mathrm{NH}}_4}^{+}$                         (B) ${{\mathrm{NH}}_2}^{+}$                          (B) ${{\mathrm{NH}}_4}^{-}$

Enter your correct answer as A, B or C.