The compound shown is 2,3-dibromopentane drawn without stereochemistry. How many stereoisomers does it have? Give an integer.

C2 carries $\mathrm{H}$, $\mathrm{Br}$, $\mathrm{CH}{}_3$ and C3; C3 carries $\mathrm{H}$, $\mathrm{Br}$, $\mathrm{C}{}_2\mathrm{H}{}_5$ and C2. Both are stereocentres. Unlike 2,3-dibromobutane, the two ends are different (methyl versus ethyl), so no meso form is possible. The total is $2^2=4$ stereoisomers, forming two pairs of enantiomers.