Volume change from gas mole ratios at constant T and P

Steps:

• Count moles of gaseous reactants: A=3, B=3, C=4, D=9.
• Count moles of gaseous products: A=2, B=3, C=2, D=10.
• Calculate percentage change: [(product moles - reactant moles)/reactant moles] × 100%.
• Compare values: A=-33%, B=0%, C=-50%, D=+11%; C shows largest decrease.

Why C is correct:

• N₂ + 3H₂ → 2NH₃ decreases moles from 4 to 2, yielding -50% volume change per Avogadro's law (V ∝ n).

Why the others are wrong:

• A: -33% change, smaller decrease than C.
• B: 0% change, volumes equal.
• D: +11% increase, volume expands.

Final answer: C