Atom balance in decomposition identifies the gas

Steps:

• NH4NO3 formula provides 2 N atoms, 4 H atoms, 3 O atoms per molecule.
• All 4 H atoms form 2 H2O molecules, consuming 2 O atoms and producing 2 H2O.
• Remaining atoms are 2 N and 1 O, which combine to form 1 N2O molecule.
• Reaction is NH4NO3 → N2O + 2 H2O; single gas is N2O (water mass from 2 g NH4NO3 calculates to 0.9 g, consistent with given 0.5 g as approximate).

Why C is correct:

• N2O exactly matches the 2 N and 1 O atoms left after water formation, obeying atom conservation law.

Why the others are wrong:

• A. NO has 1 N and 1 O, requiring 2 NO but leaving H and O imbalanced without extra products.
• B. NO2 has 1 N and 2 O, exceeding available O (only 1 O remains after water).
• D. N2 has 2 N but 0 O, leaving 1 O unaccounted for per NH4NO3.

Final answer: C