AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(A) n-Butane (C₄H₁₀) and 2-methylpropane (C₄H₁₀) are structural isomers as both have the same molecular formula C₄H₁₀ but different carbon skeletons (straight chain and branched chain).
Structural isomers must have the same molecular formula but different structures. Only option (A) satisfies this — both compounds are C₄H₁₀. Options B, C, D pair compounds with different molecular formulae, so they cannot be isomers. The textbook explicitly uses butane and 2-methylpropane (isobutane) as the example of structural isomers.