Question

which best describes the functional group in an aldehyde?
a carbonyl group inserted into the main chain
an -oh group and a carbonyl group attached to the main chain
a carbon chain with a carbonyl group bonded to one end
a carboxylic acid bonded on each side to a carbon chain

Explanation:

An aldehyde has a carbon - oxygen double bond (carbonyl group, C=O) where the carbon of the carbonyl is bonded to a hydrogen and a carbon chain. So it is a carbon chain with a carbonyl group bonded to one end.

Answer:

a carbon chain with a carbonyl group bonded to one end