The compound which has one isopropyl group is
If One methyl group is attached to the second-last carbon of the straight chain, that is called an iso group.
In option (a), (b) and (c) there are no iso groups.
The structure of 2,2,3,3-Tetramethylpentane is
The structure of 2,2-Dimethylpentane is
The structure of 2,2,3-Trimethylpentane is