Gas volumes reveal stoichiometry for carbamic acid formation Steps:

• At r.t.p., gas volumes are proportional to moles: NH₃ = 500/24,000 mol, CO₂ = 250/24,000 mol, ratio 2:1.
• Reaction: NH₃ + CO₂ → NH₂COOH (carbamic acid), requiring 1:1 mole ratio.
• CO₂ is limiting, consumes 250 cm³ NH₃ to produce NH₂COOH.
• Excess 250 cm³ NH₃ remains unreacted; only Y (new product) forms. Why B is correct:
• NH₂COOH is the formula for carbamic acid, the direct 1:1 product of gaseous NH₃ and CO₂ per reaction stoichiometry. Why the others are wrong:
• A. (NH₂)₂CO₃ suggests ammonium carbonate, needing H₂O and different ratio: 2NH₃ + CO₂ + H₂O → (NH₄)₂CO₃.
• C. (NH₂)COOH uses awkward parentheses, not standard notation for carbamic acid.
• D. NH₂COONH₂ is ammonium carbamate, requiring exact 2:1 ratio and further NH₃ addition to carbamic acid.

Final answer: B