Assertion $(A)$:The stretching of a spring is determined by the shear modulus of the material of the spring.
Reason $(R)$:A coil spring of copper has more tensile strength than a steel spring of same dimensions.
In the light of the above statements, choose the most appropriate answer from the options given below:

(Take density of sea water $=10^3 \mathrm{kgm}^{-3}$, Bulk modulus of rubber $=9 \times 10^8 \mathrm{Nm}^{-2}$, and $\mathrm{g}=10 \mathrm{~ms}^{-2}$ )