Question

Number of the following configurations showing mesoisomerism is _____.

Answer 1

Answer: 4

All compounds have two chiral centers.
(i) has a plane of symmetry $\Rightarrow$ Meso


A plane of symmetry $\Rightarrow$ Meso compound

Odd no. of interchanges produces a different compound which is symmetric.
Hence, this compound is not a meso isomer.
(v) has a plane of symmetry $\Rightarrow$ Meso

Hence, this compound is also not a meso isomer similar to (iv).
Therefore, (i), (ii), (iii) and (v) are meso isomers.