Rigid :

A. Merciful

B. Generous

C. Lenient

D. Tolerant

Answer: Option C

Solution(By Examveda Team)

Merciful : showing or exercising mercy.
Generous : showing a readiness to give more of something, especially money, than is strictly necessary or expected.
Tolerant : showing willingness to allow the existence of opinions or behaviour that one does not necessarily agree with
Lenient : more merciful or tolerant than expected, flexible.
Rigid : unable to bend or be forced out of shape, not flexible.

Appropriate antonym of Rigid is Lenient.