Structural Isomers of Butane (C4H10)

Steps:

• Confirm alkane formula CnH2n+2 gives C4H10 for n=4, requiring only carbon and hydrogen with different connectivities.
• Identify the two isomers: straight-chain n-butane (CH3CH2CH2CH3) and branched 2-methylpropane (CH3CH(CH3)CH3 or (CH3)3CH).
• Verify option formulas match C4H10 by counting atoms and ensuring hydrocarbon structure.
• Eliminate options with incorrect atom counts or non-alkane structures.

Why A is correct:

• All formulas are C4H10 alkanes; CH3CH2CH2CH3 is n-butane, while CH3CH(CH3)CH3 and (CH3)3CH both depict the branched isomer with different notation.

Why the others are wrong:

• B includes CH3CH2CH3 (C3H8, propane) and CH3OCH2CH3 (C4H10O, ether with oxygen).
• C and D provide no formulas, failing to represent any isomers.

Final answer: A