What is the bulk modulus of a perfectly rigid body?

$A$ solid sphere of radius $r$ made of a soft material of bulk modulus $K$ is surrounded by a liquid in a cylindrical container. $A$ massless piston of area $a$ floats on the surface of the liquid,covering the entire cross-section of the cylindrical container. When a mass $m$ is placed on the surface of the piston to compress the liquid,the fractional decrement in the radius of the sphere,$\left( \frac{dr}{r} \right)$ is:

The adiabatic elasticity of a gas is equal to

Bulk modulus of water is $2 \times 10^9 \ N/m^2$. The pressure required to increase the volume of water by $0.1 \%$ in $N/m^2$ is:

If the Bulk modulus of lead is $8.0 \times 10^9 \, N/m^2$ and the initial density of the lead is $11.4 \, g/cc$,then under the pressure of $2.0 \times 10^8 \, N/m^2$,the density of the lead is ............. $g/cc$.

Explain why solids are the least compressible and gases are the most compressible based on the bulk modulus.