Limonene has two C=C double bonds requiring hydrogenation

Steps:

• Calculate degree of unsaturation for C10H16: (2×10 + 2 - 16)/2 = 3.
• Subtract 1 for the 6-membered ring: 3 - 1 = 2 C=C double bonds.
• Each C=C bond reacts with 1 mol H2, so 2 mol H2 per mol limonene.
• At room conditions, 1 mol gas occupies 24 dm³, so 2 × 24 = 48 dm³.

Why C is correct:

• Matches 2 mol H2 × 24 dm³/mol (molar volume at RTP).

Why the others are wrong:

• A: Assumes 0.5 mol H2 (ignores actual double bonds).
• B: Assumes 1 mol H2 (underestimates by one double bond).
• D: Assumes 3 mol H2 (includes ring as unsaturation).

Final answer: C