It is observed that five hours are needed to dissolve a 1 cm cube of NaCl in large amount of water. Calculate the time required for dissolution, if the cube is ground to a power containing 10¹⁶ equal sized spheres. Assume that the rate of dissolution is directly proportional to initial area of contact between NaCl and water.

The mass of gas adsorbed, $\mathrm{x}$, per unit mass of adsorbate, $\mathrm{m}$, was measured at various pressures, $\mathrm{p}.$A graph between $\log \frac{\mathrm{x}}{\mathrm{m}}$ and $\log \mathrm{p}$ gives a straight line with slope equal to $2$ and the intercept equal to $0.4771$. The value of $\frac{\mathrm{x}}{\mathrm{m}}$ at a pressure of $4 \mathrm{atm}$ is :

(Given $\log 3=0.4771$)

Given:



On the basis of data given above, predict which of the following gases shows the least adsorption on a definite amount of charcoal?