Elasticity is the ability of a material to deform under stress and then return to its original shape when the stress is removed.
The restoring force in elastic materials is associated with the inter-atomic or inter-molecular forces that act to bring the atoms or molecules back to their original positions when the material is deformed. When an external force is applied to a material, it causes a displacement of atoms or molecules from their equilibrium positions. The restoring force is a result of the potential energy stored in these inter-atomic or inter-molecular bonds, and it works to bring the material back to its original state.
Hence, both (A) and (R) are true and (R) is the correct explanation (A)