Optical isomers have the same physical properties: Melting point, boiling point, density etc. They have the same specific rotations but with opposite signs. Three forms of lactic acid are known, of which two are optically active and the third one is optically inactive.

Why are optical isomers optically active?

Simple substances which show optical isomerism exist as two isomers known as enantiomers. A solution of one enantiomer rotates the plane of polarisation in a clockwise direction. ... When optically active substances are made in the lab, they often occur as a 50/50 mixture of the two enantiomers.

Can an enantiomer be optically inactive?

Enantiomers will rotate the plane of polarisation in exactly equal amounts (same magnitude) but in opposite directions. ... For example, a 50:50 mixture of two enantiomers or a racemic mixture will not rotate plane polarised light and is optically inactive.