Alcohols are isomers if they share the same molecular formula but differ in structure

Steps:

• Define isomers as compounds with identical molecular formulas but different arrangements of atoms.
• Determine the molecular formula for each alcohol by counting carbons and hydrogens, adding the OH group.
• Compare formulas within each option's pair to check for matches.
• Confirm structural differences for the matching pair to verify isomerism.

Why A is correct:

• Both butan-1-ol (CH₃CH₂CH₂CH₂OH) and 2-methylpropan-1-ol ((CH₃)₂CHCH₂OH) have the formula C₄H₁₀O, with straight-chain vs. branched structures.

Why the others are wrong:

• B: Pentan-1-ol is C₅H₁₂O while 2-methylpropan-1-ol is C₄H₁₀O; different carbon atoms.
• C: Propan-1-ol is C₃H₈O while 2-methylpropan-1-ol is C₄H₁₀O; mismatched formulas.
• D: Propan-2-ol is C₃H₈O while 2-methylpropan-2-ol is C₄H₁₀O; unequal molecular formulas.

Final answer: A