The pressure of real gases is less than that of ideal gas because of:

Consider the equation $Z = \frac{pV}{RT}$. Which of the following statements is correct?

Statement $-1$: The compressibility factor at the critical point is the same for different gases following van der Waal's equation.
Statement $-2$: The compressibility factor is independent of pressure at the critical temperature.

At relatively high pressure,the van der Waals equation reduces to

When helium gas is allowed to expand into vacuum, a heating effect is observed. The reason for this is (assume $He$ as a non-ideal gas):

The compressibility factor $Z = \frac{pV}{nRT}$ for hydrogen gas at $273 \ K$ and $1 \ atm$ pressure is