[coooool222]

I answered A and B but I don't get C. What do they mean by identical conditions?
I attached the screenshot of the problem

[Borek]

Same P, T in both cases.

[coooool222]

Then wouldn't the volume be the same?

[AWK]

The question is far from being precise. If p and V are not given, the standard terms are usually taken. But under these conditions, the water will almost completely condense. So the question of water vapor volume does not make sense. But if the temperature was, for example, 150°C, this question makes sense and can be calculated even without a calculator.

[mjc123]

Your answer to part B is incomplete. The question asks for the mass of P₄O₁₀.