Which of the following compounds are optically inactive but exhibit geometrical isomerism?

A compound incapable of optical rotation is said to be optically inactive . All pure achiral compounds are optically inactive.

eg: Chloroethane (1) is achiral and does not rotate the plane of plane-polarized light.

In order to be optically inactive no net rotation, each molecule in a sample must have a second molecule positioned as its mirror image. One enantiomer will rotate light in a clockwise direction and is designated as the (+) isomer. It is also called the dextrorotatory dexter = right isomer. Look for an internal plane, or internal mirror, that lies in between the compound. The stereochemistry e.g. R or S is very crucial in determining whether it is a meso compound or not. As mentioned above, a meso compound is optically inactive, so its stereochemistry should cancel out.

From the above image option, a, b and c are optically inactive when a plane of polarized light is sent. and option d is optically active.

and A, b and c are geometric isomers.

Hence, correct option is (a), (b) and (c).