The correct answer is C. 40 x 105 kg/cm2.
The bulk modulus of elasticity is a measure of how difficult it is to compress a material. It is defined as the ratio of the pressure applied to a material to the fractional change in volume that results. In this case, the pressure is increased from 50 kg/cm2 to 150 kg/cm2, and the volume decreases from 0.04 m3 to 0.039 m3. This means that the fractional change in volume is $\frac{0.04 \text{ m}^3 – 0.039 \text{ m}^3}{0.04 \text{ m}^3} = 0.025$. The bulk modulus of elasticity is then $B = \frac{P}{\Delta V/V} = \frac{150 \text{ kg}/\text{cm}^2}{0.025} = 40 \times 10^5 \text{ kg}/\text{cm}^2$.
Option A is incorrect because it is the pressure applied to the material, not the bulk modulus of elasticity. Option B is incorrect because it is the bulk modulus of elasticity of a different material. Option D is incorrect because it is too large.