The container under the piston contains water and steam. The volume of the vessel is slowly increased isothermally

The container under the piston contains water and steam. The volume of the vessel is slowly increased isothermally, while there is still water in the vessel. How do the mass of steam and its pressure change?

Given:
Isothermal process;
The volume is increasing;
Find the change in mass and pressure in the vessel;
Decision:
In an isothermal process, the temperature is constant, that is, T = const, p * V = const:
If T = const, then with increasing volume, the pressure p decreases.
The mass of steam does not change, since the process is isothermal.
Answer: The mass m does not change, the pressure p decreases.