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

Functional group isomerism is a type of isomerism where molecules that have same molecular formula but can exhibit different functional groups in their structural formula. Alcohols(-OH) and ethers (-O-)can have same molecular formula but can exhibit different functional groups. Aldehydes(-CHO) can give functional group isomer as ketones(C=O). Cyanides(-CN) can form functional group isomer iso- cyanide(-NC). While Alkyl halides can exhibit chain and position isomerism they cannot exhibit functional group isomerism.