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Which of the following statements correctly describe a real gas at high pressure and room temperature?

1. Z > 1
2. Z = 1 + a / (R * T * Vm)
3. Z = 1 + P*b / (R*T)
4. Repulsive forces are dominant

Correct answer: Z > 1

Solution

At high pressure, intermolecular distances are small and repulsive interactions dominate. The van der Waals compressibility factor simplifies to Z approximately 1 + Pb/(RT), which is greater than 1 since b > 0. Option A (Z > 1) and options C (Z = 1 + Pb/RT) and D (repulsive forces dominant) are all correct. Option B (with -a term) applies at low pressure / high temperature, not high pressure.

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