The compound shown is $(R)$-2-chlorobutane. Which of the wedge drawings shown as options is its enantiomer?

An enantiomer must have the same constitution and the opposite configuration. R is 2-bromobutane and S is butan-2-ol, different compounds, so they are excluded whatever their descriptors. P is 2-chlorobutane drawn from a different angle, but applying $\mathrm{Cl}>\mathrm{C}{}_2\mathrm{H}{}_5>\mathrm{CH}{}_3>\mathrm{H}$ gives $(R)$ again, so P is the same compound. Q is 2-chlorobutane with the $(S)$ configuration, so Q is the enantiomer.