Answer : The correct option is, (C) a carbon chain with a carbonyl group bonded to one end.
Explanation :
An aldehyde is an organic compound which contain a functional group with (-CHO) i.e R-CHO
R-CHO functional group consists of a carbonyl center that means a carbon which is double-bonded to the oxygen. The carbon of this carbonyl group bonded with the hydrogen to one end and a carbon chain, (R) to another end.
Some examples of an aldehydes are formaldehyde
, acetaldehyde

Therefore, the correct answer is, (C)