Assertion (A): Steel is more elastic than rubber.
Reason (R): Under a given deforming force, steel is deformed less than rubber.
(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 reason is not correct explanation of the assertion
(C) Assertion is true, but the reason is false
(D) Assertion is false but the reason is true

Hint
Elasticity of a body is given by its Young’s Modulus, the higher the Young’s Modulus the higher the elasticity. Young Modulus of a material is given by the deforming stress divided by the resulting strain.

Complete step by step answer
In daily life, when people speak of elasticity, they mean the ability of a body to return to its original shape after some form of deformation. However, in physics or engineering, the elasticity of a body is measured by the stress required to generate a specified strain, i.e. how much force will be required to cause a particular extension. If the force required for a certain deformation is large, then the substance is highly elastic, if the force is little, then it is not very elastic.
Conversely, it can be said that elasticity is measured by the strain caused due to a particular deforming force. When the strain is low, elasticity is high and when the strain is high, elasticity is low.
Hence, considering from prior knowledge and experience, for a particular force exerted to stretch the substance, rubber extends far more than steel. This implies that for a given deforming force, steel deforms less than rubber. Comparing this with the above explanation, we can conclude that steel is more elastic than rubber because steel deforms less than rubber.
Thus, option (A) is the correct option.

Note
Hence, from the descriptions above, in application, elastic materials like steel and iron, in general are used where strength or the ability to withstand large forces, without much deformation, are required, such as in ships, buildings etc. The less elastic materials like rubber and plastic are used where considerable deformation is desired in the design of the structure. These include tyres, balloons, trampolines etc.