Here's the question.
A window in the room is open. The next day, the temperature of the room has increased, but the pressure of the air stayed the same. State and explain what has happened to the mass of air in the room.
The model answer , which I don't understand really well: mass (of air) in room decreases B1 (because) air expands / vol of air increases / density of air decreases / appropriate use of pV = nRT OR pressure argument e.g. pressure would have increased (with constant volume) if mass constant B1 any ONE from: B1 some air leaves room molecules collide harder or more (often) molecules move faster / have more energy molecules move further apart NOT molecules expand
I'd appreciate it if someone could explain it because the model answer is very misleading.