Internal radius of a capillary tube is $\frac{1}{28} \mathrm{cm}$ and surface tension of water is $70 \mathrm{dyne} {\mathrm{cm}}^{-1}$. If the angle of contact is zero, then water will rise up in the tube up to a height,

Adding detergents to water helps in removing dirty greasy stains. This is because,

(a) it increases the oil-water surface tension.
(b) it decreases the oil-water surface tension.
(c) it increases the viscosity of the solution.
(d) dirt is held suspended surrounded by detergent molecules.