Hydrogen atoms from NH3 and HCl in decomposition

Steps:

• The reaction NH4Cl(s) → NH3(g) + HCl(g) produces 2 gas molecules per formula unit.
• Total gas molecules = 2.4 × 10^{24}, so formula units decomposed = 2.4 × 10^{24} / 2 = 1.2 × 10^{24}.
• Each NH3 has 3 H atoms; each HCl has 1 H atom; total 4 H atoms per formula unit.
• Total H atoms = 4 × 1.2 × 10^{24} = 4.8 × 10^{24}.

Why C is correct:

• Matches calculation of 4 H atoms per 2 gas molecules from the balanced equation.

Why the others are wrong:

• A: Counts only 2 H atoms per decomposition, ignoring NH3's 3 H.
• B: Equals total gas molecules, not H atoms.
• D: Assumes 8 H atoms per decomposition, double the actual.

Final answer: C