The bromoalkane shown is treated with sodium in dry ether and gives the coupled alkane. How many stereoisomers does this coupled alkane have (count the meso form once and each enantiomer separately)?

The compound shown is 2-bromobutane. Wurtz coupling gives 3,4-dimethylhexane, which has two similar stereocentres (C3 and C4). The configurational isomers are (3R,4R), (3S,4S) and the meso (3R,4S), which is identical to (3S,4R). That is 3 stereoisomers, not 4, because the meso form is counted once.