Equilibrium in limiting reactant reversible reaction

Steps:

• Reaction is X + 2Y ⇌ XY₂; initial: 1 mol X, 1 mol Y (Y limiting, max 0.5 mol XY₂).
• Let ξ be moles of XY₂ at equilibrium; then X = 1 - ξ, Y = 1 - 2ξ, XY₂ = ξ.
• ξ ≤ 0.5; for finite K, ξ < 0.5 to maintain reverse rate, so X > 0.5 mol and XY₂ < 0.5 mol < 1 mol.
• Statement 1 false: rates equal but reaction continues; 2 and 3 true.

Why D is correct:

• Limiting Y and reversibility ensure XY₂ < 1 mol (max 0.5) and X > 0.5 mol (ξ < 0.5), per equilibrium constant definition.

Why the others are wrong:

• A: Includes false statement 1 (equilibrium means equal rates, not stop).
• B: Misses true statement 3 (X > 0.5 mol due to incomplete reaction).
• C: Misses true statement 2 (XY₂ < 1 mol from stoichiometry).

Final answer: D