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The compounds with atleast two stereogenic centers and a plane of symmetry are termed meso compounds.

The meso compounds are achiral.

There are two planes of symmetry as follows:

• The horizontal plane of symmetry bisects the horizontal plane into two equal halves.
• The vertical plane of symmetry bisects the vertical plane into two equal halves.

a. The given compound has two stereogenic centers (as two centers have four different groups), and it has the same substituents with the same stereochemistry.

Therefore, a vertical plane of symmetry exists in this compound. Hence, the compound is a meso compound.

Meso compound with a vertical plane of symmetry

b. The given compound has 2 stereogenic centers (as two centers have four different groups), but it does not have the substituents with the same stereochemistry.

Therefore, a plane of symmetry does not exist in this compound. Hence, the compound is not a meso compound.

Not a meso compound

c. The given compound also has 2 stereogenic centers, and it has the same substituents with the same stereochemistry.

Therefore, a vertical plane of symmetry exits in this compound. Hence, the compound is a meso compound.

Meso compound with a vertical plane of symmetry