Which of the following is chiral?

C2 of 2-deuteriobutane carries $\mathrm{H}$, $\mathrm{D}$, $\mathrm{CH}{}_3$ and $\mathrm{C}{}_2\mathrm{H}{}_5$, four distinguishable groups, so it is a (very weakly active) chiral molecule. In 3-methylpentane and 3-chloropentane the stereogenic candidate has two identical ethyl groups, and in 2-chloro-2-methylbutane the candidate carbon has two identical methyl groups, so all three are achiral.