Carbon Percentage and Isomers in Alkanes

Steps:

• Methane (CH4) has molar mass 16 g/mol, carbon mass 12 g/mol, so %C = (12/16) × 100 = 75%.
• Butane (C4H10) has molar mass 58 g/mol, carbon mass 48 g/mol, so %C = (48/58) × 100 ≈ 82.8%.
• Statement 1 is false because butane has a higher carbon percentage than methane.
• Statement 2 is true: n-butane and isobutane (2-methylpropane) are the two isomers of C4H10.

Why C is correct:

• It selects only statement 2, which accurately identifies the two constitutional isomers of C4H10 per organic chemistry nomenclature.

Why the others are wrong:

• A includes the false statement 1 on carbon percentage.
• B selects only the incorrect statement 1.
• D excludes the true statement 2 on isomers.

Final answer: C