Which one of the structures shown is chiral? Consider configuration only (rings treated as planar).

(A) cis-1,2-dichlorocyclopropane has a mirror plane through C3, so it is meso and achiral. (B) trans-1,2-dichlorocyclopropane has the two Cl atoms on opposite faces; the two stereocentres have the same descriptor, there is no mirror plane, and the compound is chiral (one of a pair of enantiomers). (C) 1,1-dichlorocyclopropane has no stereocentre. (D) cis-1,3-dimethylcyclobutane has a mirror plane through C1 and C3 and is achiral. Only (B) is chiral.