The diagram shows two flasks X and Y connected by a thin tube of negligible volume - AQA - A-Level Physics - Question 8 - 2020 - Paper 2

To find the mass of gas in flask Y, we can use the ideal gas law and the relationship between pressure, volume, and temperature. Since flask X has a volume that is double that of flask Y, we set the volume of Y as V and the volume of X as 2V.

Using the ideal gas law, we can relate the densities and temperatures:

Let the density of the gas in X be given by: $\rho_X = \frac{m}{2V}$

And the density of gas in Y by: $\rho_Y = \frac{M}{V}$

From the relation of gases at different temperatures and volumes, knowing that the pressure remains constant, we can write the relation:

$\frac{\rho_X}{T_X} = \frac{\rho_Y}{T_Y}$

Plugging in the values:

$\frac{\frac{m}{2V}}{100} = \frac{M}{V \cdot 400}$

Cross-multiplying gives:

$400m = 200M$

Rearranging leads to:

$M = 2m$

Thus, the mass of gas in flask Y is (2m).