The question can be explained by Graham's law of diffusion. According to this law, under the same conditions of temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its molar mass.

\(\frac{R_x}{R_y}\) = \(\sqrt{\frac{M_y}{M_x}}\)

From the question, Gas X diffuses twice as fast as gas Y  i.e  x = 2y

This implies x =2 while y = 1

From \(\frac{R_x}{R_y}\) = \(\sqrt{\frac{M_y}{M_x}}\)

 \(\frac{2}{1}\) = \(\sqrt{\frac{M_y}{M_x}}\)

 \(\frac{4}{1}\) = \(\frac{M_y}{M_x}\)

 M\(_y\) = 4 M\(_x\)

⇒ Gas Y is 4 times as heavy as Gas X. - Option B