The porosity is measured by

Answer: Option C

Porosity is the measure of empty spaces in the soil. The porosity of the surface soil usually decreases as the size of the particle increases. The porosity of subsoil is lower than the surface soil due to compaction by gravity.
It can be measured by the formulae:
$$\mathbf{P}=100-\left(\frac{\mathbf{Bulk}\mathbf{Density}}{\mathbf{Particle}\mathbf{Density}}\right)\times 100$$