Which among the following is a pair of functional isomers?

Step-by-step solution

Functional isomers are compounds sharing the same molecular formula but differing in their functional groups. Option B satisfies this criterion as the two compounds are both C ₄ H ₁₀ O but contain alcohol and ether groups respectively. Butan-1-ol ( CH ₃ CH ₂ CH ₂ CH ₂ OH ) is an alcohol, while 1-methoxypropane ( CH ₃ OCH ₂ CH ₂ CH ₃ ) is an ether. The remaining options involve pairs that are isomers but share the same functional group, such as alcohols (A) or ethers (C and D), making them positional or chain isomer