When a clock's minute hand moves, its shaft twists slightly, generating a torque proportional to the angle of twist. What physical property determines the torque in the clock's shaft?

Correct option is B

​$$\text{When the clock's shaft twists by a small angle, it behaves like a torsional spring.} \\[6pt]\text{The restoring torque } \tau \text{ is given by:} \\[6pt]\tau = k_t \, \theta \\[8pt]\text{where:} \\[4pt]\bullet \ k_t = \text{ torsional stiffness of the shaft} \\[2pt]\bullet \ \theta = \text{ angle of twist} \\[8pt]\text{Thus, the torque generated is directly proportional to the torsional stiffness, which depends on:} \\[6pt]\bullet \ \text{Material's shear modulus} \\[2pt]\bullet \ \text{Shaft geometry (length and polar moment of inertia)}$$​​