(A) : For a perfectly incompressible substance, bulk modulus is infinity 

(R) : Bulk modulus of elasticity is inversely proportional to change in volume.

The bulk modulus of the material that makes up the body is what is used when the volume strain is minor compared to the normal stress

$\mathrm{B}=\frac{\mathrm{normal} \mathrm{stress}}{\mathrm{volume} \mathrm{strain}}$.

The liquid is incompressible, hence the volume change is zero.

$\mathrm{B}=\frac{\mathrm{normal} \mathrm{stress}}{0}=\infty$

The bulk modulus of elasticity gauges how well a body can expand back to its original size after being crushed. It therefore symbolises the material's incompressibility.

$\mathrm{K}=\frac{-\mathrm{PV}}{∆\mathrm{V}}$
Thus elasticity is inversely proportional to change in volume.

Hence the correct answer is Both ‘A’ and ‘R’ are true and ‘R’ is the correct explanation of ‘A’.