Step 1:
- NO$_2^-$ : two bond pairs + one lone pair = 3 domains → sp$^2$?
But structure angular with one lone → effectively sp.
- NO$_3^-$ : 3 sigma bonds = 3 domains → sp$^2$.
- NH$_4^+$ : 4 sigma = 4 domains → sp$^3$.
Step 2: Compare options → (A).