Question

How and why do we represent the reduction of a the nitro group to give ammonia in acidic conditions?

Answer 1

Because you might not be able to get the metals/salts up into solution in a basic or neutral medium.

Explanation:

I presume you want to effect the reduction of a nitro group, `NO_2^(-)` to ammonia?

We could write the redox reaction as........`stackrel(+III)N+6e^(-)rarrstackrel(-III)N`

`NO_2^(-) +8H^(+) + 6e^(-) rarr NH_4^+ +2H_2O`

The conditions are a matter for investigation by experiment. And of course we need an electron source, a metal or metal salt capable of oxidation. A metal salt MAY not have sufficient solubility in an alkaline medium.