Mass of chlorine gas using moles and molar mass

Steps:

• Chlorine gas is diatomic (Cl₂), so its molar mass is twice the atomic mass of Cl (35.5 g/mol × 2 = 71 g/mol).
• Use the formula: mass = moles × molar mass.
• For 2 mol of Cl₂: mass = 2 × 71 g/mol = 142 g.

Why D is correct:

• Mass equals moles times molar mass (71 g/mol for Cl₂), yielding 142 g for 2 mol per the mole concept in chemistry.

Why the others are wrong:

• A: 17.5 g is half the atomic mass of Cl, irrelevant to Cl₂ gas.
• B: 35.5 g is the atomic mass of one Cl atom, not for molecular Cl₂.
• C: 71 g is the mass of 1 mol of Cl₂, not 2 mol.

Final answer: D