In which of the following, functional group isomerism in not possible?

Alcohols and ethers, aldehydes and ketones, cyanides and isocyanides, carboxylic acids are functional isomers, whereas in the case of Alkyl halides functional group isomerism is not possible.Alkyl Halides are also KNOWN as Haloalkanes and they never show functional group isomerism because there’s only ONE way to attach a halogen to a carbon chain and that is via one single BOND. Halogens can’t form more than one bond in the context of common organic compounds, and can’t form multiple bonds to carbon.The PHENOMENON of the existence of two or more compounds possessing the same molecular formula but DIFFERENT properties is known as Isomerism.Two or more compounds having the same molecular formula but different functional groups are called functional isomers and this phenomenon is termed as functional group isomerism.