(a) Incorrect. This is because if steel and rubber wires of same length and area of cross-section are subjected to same deforming force, then the extension produced in steel is less than the extension produced in rubber, In other words, for producing same strain in steel and rubber, more stress is required in case of steel.
(b) Correct. The reason is that when a coil spring is stretched, there is neither a change in the length of the coil (i.e., length of the wire forming the coil spring) nor a change in its volume. Since the change takes place in the shape of the coil spring, its stretching is determined by its shear modulus.