What is the common name of the given compound?

The correct answer is Option (4) → Cinnamaldehyde

The given compound has a benzene ring joined to a three-carbon chain that carries a C=C double bond and ends in an aldehyde group: \( \ce{C6H5-CH=CH-CHO} \). Its IUPAC name is 3-phenylprop-2-enal. It is the compound that gives cinnamon its smell and flavour, and its common name is cinnamaldehyde.

NCERT (2026-27 edition):
Aldehydes, Ketones and Carboxylic Acids – “… They add fragrance and flavour to nature, for example, vanillin (from vanilla beans), salicylaldehyde (from meadow sweet) and cinnamaldehyde (from cinnamon) have very pleasant fragrances.”