Read the assertion and reason carefully to mark the correct option out of the options given below:
Assertion: The stretching of a coil is determined by its shear modulus.
Reason: Shear modulus changes only the shape of a body keeping its dimensions unchanged.
A. Both assertion and reason are true and the reason is the correct explanation of the assertion.
B. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
C. The assertion is true but the reason is false.
D. The assertion and reason both are false.
E. The assertion is false but the reason is true.

Hint: Before we start answering let’s understand the shear modulus. The shear modulus is the measure of the deformation of a solid.

Complete step by step solution:
If a force is applied parallel to one surface of solid material, while an opposing force acts on its opposite surface and holds the solid material in place results in the deformation of a solid material. As you start stretching the spring, the windings of the coil go apart from the original position.

Here only there is a change in the shape of the spring but the length of the wire remains the same. In other words, it's just twisting the wire as the spring stretches.So, we can conclude that both assertion and reason are true and the reason is the correct explanation of the assertion.

Hence, option A is the correct answer.

Note:Modulus of elasticity is defined as the ratio of stress to corresponding strain within elastic limits. There are three types of moduli of elasticity : Bulk modulus, rigidity modulus, and Young modulus.