Decide parent chain.

Numbering so that more substituted substituent will get the lowest number.

Five carbons $\Rightarrow$ word root = pent

                                    single bonds = ane(suffix)

$\to$ substituent at $C_{2}and{C}_3$

$\Rightarrow$ 3-ethyl-2, 3-dimethylpentane(alphabetically)

Therefore,

                (b) 3-Ethyl-2,3-dimethylpentane