The main carbon chain has 3 carbon atoms, so it is ‘prop’, and the carbon adjacent to the N atom would be named as 1. Then there is one double bond in the second carbon position (en) and 1 N-methyl amine in the first carbon position.

Therefore IUPAC name is N-methylprop-2-en-1-amine.

The common name for this compound is allylmethylamine.

2-amino-4-pentene has 5 carbon atoms in the main chain.