Stoichiometry of Mg(NO3)2 decomposition to NO2

Steps:

• Calculate moles of Mg(NO3)2: molar mass 148 g/mol, so 7.4 g / 148 g/mol = 0.05 mol.
• Decomposition: 2Mg(NO3)2 → 2MgO + 4NO2 + O2, so 1 mol Mg(NO3)2 yields 2 mol NO2 (X).
• Moles of NO2: 0.05 mol × 2 = 0.1 mol.
• Mass of NO2: 0.1 mol × 46 g/mol = 4.6 g.

Why D is correct:

• Matches exact stoichiometric mass of NO2 from 0.05 mol Mg(NO3)2 using 2:1 mole ratio and 46 g/mol molar mass.

Why the others are wrong:

• A: Assumes 1:1 mole ratio, underestimating NO2 by half.
• B: Uses incorrect NO molar mass (30 g/mol) instead of NO2.
• C: Assumes 1 mol NO2 per mol Mg(NO3)2 with wrong molar mass.

Final answer: D