Assertion (A): the anti-staggered conformation of meso-2,3-dibromobutane is achiral. Reason (R): in the anti-staggered conformation the molecule has a centre of inversion.

ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
DA is false but R is true

Answer: A

In the anti conformation of the (2R,3S) isomer the two Br, the two

CH X_{3}

and the two H are each anti to their partners, so the molecule has an inversion centre at the midpoint of the C-C bond. A molecule with a centre of inversion is superimposable on its mirror image, i.e. achiral. Both statements are true and R is the explanation.

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