Question

What is the correct name of the compound with the formula `NH_4NO_2`?

Answer 1

Ammonium nitrite

Explanation:

Since nitrogen - in an acid form - has two oxidation numbers, the higher (+5) is reserved for "nitrate" (like in nitric acid) and the lower (+3) get the name "nitrite" (nitrous acid).
The nitrogen in the ammonium-ion plays a completely different role.