## To write the formula for an aldehyde, you start with the hydrocarbon chain and then add the CHO group at the end.

The general formula for an aldehyde can be represented as:

R-CHO

R represents the hydrocarbon chain, which can vary in length and structure. The CHO group consists of a carbon atom (C) bonded to a hydrogen atom (H) and an oxygen atom (O).

For example, let's consider ethanal, also known as acetaldehyde. In this case, the hydrocarbon chain (R) is just a single carbon atom. Therefore, the formula for ethanal is:

CH3-CHO

I hope this explanation clarifies how to construct the formula for an aldehyde.