Question

The rate of diffusion of gas is:
A. Directly proportional to its density
B. Directly proportional to its molecular weight
C. Directly proportional to the square root of its molecular weight
D. Inversely proportional to the square root of its molecular weight

Answer 1

Hint: Diffusion is basically a process of movement of molecules under a concentration process and important in all living beings. This process helps the substances to move out and to move in the cells.

Complete answer:
During the process of diffusion molecules move from a region of higher concentration to the region of lower concentration until the concentration remains equal throughout the process.
Rate of diffusion can be explained by Graham’s law of diffusion. This law states that the rate at which a gas diffuses is inversely proportional to the density of the gas and we know that density is given by the mass by volume. Rate of diffusion of gas can be represented by the formula:
$rate\ \text{of diffusion of gas = }\dfrac{Volume\ \text{of the gas diffusion}}{time\ \text{taken}}$
$r\propto \dfrac{1}{\sqrt{d}}$
$\dfrac{{{r}_{_{1}}}}{{{r}_{2}}}\text{ = }\sqrt{\dfrac{{{d}_{2}}}{{{d}_{1}}}}$
Since the vapor density is M/2 (molar mass)
$\dfrac{{{r}_{_{1}}}}{{{r}_{2}}}\text{ = }\sqrt{\dfrac{{{M}_{2}}}{{{M}_{1}}}}$
Here r represents the rate of diffusion and M represents the molecular weight and from the above formula we find that it is inversely proportional to the square root of its molecular weight.

Hence option D is the correct answer.

Note:
Only liquids and gases are able to undergo through the process of diffusion as only in liquids and gases molecules are free to move. Diffusion is of two types like simple diffusion and facilitated diffusion. And the process which is opposite to diffusion is known as effusion.