Modulus of rigidity of an incompressible liquid is

The modulus of rigidity, also known as the shear modulus ($G$), is defined as the ratio of shear stress to shear strain. For a fluid, shear stress is proportional to the rate of shear strain, not the shear strain itself. When a static shear force is applied to a liquid, it continues to deform indefinitely as long as the force is applied, meaning the shear strain is not defined for a static state. Consequently, the resistance to shear deformation in a liquid is zero. Therefore, the modulus of rigidity for any liquid, including an incompressible one, is zero.

Answer: Zero