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# Optical and isomers are compounds which contain the same number and kinds of atoms, and bonds (ie the connectivity between atoms is the same), and different spatial arrangements of the atoms, but which have non-super imposable mirror images. Each non-super imposable mirror image structure is called an enantiomer. Optical isomers get their name because the plane – polarized light that is passed through a sample of a pure enantiomers is rotated. The planeis rotated in the opposite direction but with the same magnitude when plane- polarized light is passed through a pure sample containing the other enantiomer of a pair. A solution of one enantiomer rotates the plane of polrisation in a clockwise direction. This enantiomer is known as the (+) form. A solution of the other enantiomer rotales the plane of polarisation in an anti-clockwise direction. This enantiomer is known as (-) form.

If the solution are equally  concentrated the amount of rototation caused by the two isomers is exactly the same , but in opposite directions. When optically active substance are made in the lab, they  often occurs as a 50/50 mixture of the two enantiopmers. This is known as a racemic mixture or racemate. It has no effect on plane polarised light.

Enantiomers have :

(a) Identical melting point / boiling point but different refractive indices

(b) Identical melting point / boiling point refractive indices but rotate plane polarised light in opposite directions but to the same extent.

(c) Different refractive indices and rotates plane polarized light in the same direction but to different extends

(d) Different melting/ boiling points but rotate plane of polarised light in different directions but to the same extends.

Enantiomers have same melting boiling point and refractive indices but rotate plane polarised light in opposite direction but to the same extent.
So, Identical melting point / boiling point refractive indices but rotate plane polarised light in opposite directions but to the same extent.
Hence b is the correct answer.