The modulus of rigidity of the ideal liquid is:
1. infinity
2. zero
3. unity
4. some finite small non-zero constant value
Hint: Ideal fluids provide no resistance to shear forces.
Explanation: No frictional (viscous) force exists in the case of an ideal fluid, hence, tangential forces are zero, so there is no stress developed. The modulus of rigidity measures a material's resistance to shear deformation. For solids, it is a finite value because they can resist shear forces. However, ideal liquids cannot resist shear forces; they flow under any applied shear stress, meaning their modulus of rigidity is effectively zero.
Hence, option (2) is the correct answer.
