a Butane and IsobutaneType of isomerism: Structural isomerism specifically, chain isomerism Explanation: Both butane and isobutane have the molecular formula C4H10, but they have different structures. Butane has a straight chain of four carbon atoms, while isobutane has a branched chain with three carbon atoms in the main chain and one carbon atom branching off the central carbon. The different arrangement of carbon atoms in the chain leads to chain isomerism.b Ethanol and Dimethyl EtherType of isomerism: Functional group isomerismExplanation: Ethanol C2H5OH and dimethyl ether CH3OCH3 have the same molecular formula, C2H6O, but they have different functional groups. Ethanol has a hydroxyl group -OH attached to a carbon atom, making it an alcohol, while dimethyl ether has an oxygen atom connected to two methyl groups, making it an ether. The different functional groups in these molecules result in functional group isomerism.c Propanoic acid and Methyl ethanoateType of isomerism: Functional group isomerismExplanation: Propanoic acid C2H5COOH and methyl ethanoate CH3COOCH3 have the same molecular formula, C3H6O2, but they have different functional groups. Propanoic acid has a carboxyl group -COOH attached to a two-carbon chain, making it a carboxylic acid, while methyl ethanoate has an ester group -COO- connecting a methyl group and an ethyl group, making it an ester. The different functional groups in these molecules result in functional group isomerism.