Consider two reactions:
$(I) \, Zn + \text{conc. } HNO_3 \text{ (hot)} \to Zn(NO_3)_2 + X + H_2O$
$(II) \, Zn + \text{dil. } HNO_3 \text{ (cold)} \to Zn(NO_3)_2 + Y + H_2O$
Compound $X$ and $Y$ are respectively:

• A
  $N_2O, NO$
• B
  $NO_2, N_2O$
• C
  $N_2, N_2O$
• D
  $NO_2, NO$