If a compound does not affect the plane of plane polarized light when passed through it. What will be the compound known as?

Optically inactive

The correct answer is (4) Optically inactive.

A compound that does not affect the plane of plane polarized light when passed through it is said to be optically inactive. This means that the compound does not have any chiral centers, which are atoms with four different groups attached to them. Chiral centers are the reason why some compounds are optically active, while others are not.

Optically active compounds can rotate the plane of plane polarized light to the right (dextrorotatory) or to the left (laevorotatory). The amount of rotation is measured in degrees and is called the specific rotation.

So, if a compound does not affect the plane of plane polarized light, it is said to be optically inactive.