Assertion (A): meso-2,3-Dibromobutane is optically inactive although it contains two stereocentres. Reason (R): The molecule has an internal plane of symmetry, so it is superimposable on its mirror image.

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

The two stereocentres of the meso form have opposite configurations,

(2 R, 3 S)

. An internal mirror plane makes the molecule identical to its mirror image, so it is achiral and optically inactive. Hence both statements are true and R explains A.

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Assertion (A): meso-2,3-Dibromobutane is optically inactive although it contains two stereocentres. Reason (R): The molecule has an internal plane of symmetry, so it is superimposable on its mirror image.

Answer: A

More questions on Chirality, enantiomers and R/S configuration