Answer:
Formaldehyde.
Step-by-step explanation:
An aldehyde is a carbonyl compound where there is at least on hydrogen is bonded to carbonyl carbon.
The simplest aldehyde or first member of aldehydes the carbonyl carbon is bonded to two hydrogens. As we move up in the homologous series of aldehydes there is addition of one carbon in place of one of the hydrogen.
The structure are shown in figure.