Answer
Option (b).
Work Step by Step
The longest chain of carbon with -CO- as a functional group is assigned, and gives it a base name. In the given structure, the longest carbon chain has five carbon atoms. So, the base name is pentanone. The number is assigned in a way that the -CO- functional group gets the lowest number.
So, the -CO- functional group is situated at the second position. Therefore, the name of the compound is 2-pentanone .
