Which of the following is a requirement for a rigid body to be in mechanical equilibrium?
For mechanical equilibrium, both translational and rotational equilibrium are required: the net force (∑F = 0) and net torque (∑τ = 0) must be zero. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Both net force and net torque must be zero. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.
Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.