Match each compound in Column I with its total number of stereoisomers in Column II. Column I: (P) butane-2,3-diol; (Q) pentane-2,3-diol; (R) hexane-2,3,4-triol, $CH X_{3} - CH (OH) - CH (OH) - CH (OH) - CH X_{2} - CH X_{3}$ ; (S) 2-bromobutane. Column II: (1) 2; (2) 3; (3) 4; (4) 8.

Answer: A

Butane-2,3-diol is symmetric, so it has (R,R), (S,S) and meso, i.e. 3 stereoisomers. Pentane-2,3-diol has two different stereocentres, so

2^{2} = 4

. Hexane-2,3,4-triol has three different centres in an unsymmetrical chain, so

2^{3} = 8

. 2-Bromobutane has one stereocentre, so 2. The match is P-2, Q-3, R-4, S-1.