Molar Mass of Diatomic Chlorine Gas

Steps:

• Chlorine gas exists as Cl₂ molecules, so relative molecular mass = 2 × 35.5 = 71.
• Molar mass of Cl₂ = 71 g/mol.
• Mass of 2 mol of Cl₂ = 2 × 71 g/mol = 142 g.

Why D is correct:

• By definition, the mass of n moles of a substance equals n times its molar mass; here, 2 mol × 71 g/mol = 142 g for Cl₂.

Why the others are wrong:

• A: 17.5 g is half the atomic mass of chlorine, irrelevant to moles of gas.
• B: 35.5 g is the mass of 1 mol of chlorine atoms, not diatomic gas.
• C: 71 g is the mass of 1 mol of Cl₂, not 2 mol.

Final answer: D