The aldehyde which is formed during photosynthesis of plants is

Methanal

The aldehyde which is formed during photosynthesis of plants is (2) methanal (formaldehyde).

Methanal is a simple aldehyde with the formula \(HCHO\). It is a colorless, flammable gas with a pungent odor. It is produced naturally during the process of photosynthesis, and it is also used in a variety of industrial applications.

Propanal, acetaldehyde, and phenylmethanal are all aldehydes, but they are not formed during photosynthesis. Propanal is a three-carbon aldehyde, acetaldehyde is a two-carbon aldehyde, and phenylmethanal is a benzene derivative with an aldehyde group.