Which of the following observations indicates that attractive forces may exist between gas molecules?
X. Doubling the pressure on H2(g) results in halving of its volume.
Y. The measured molar volume of Cl2(g) is < 22.4 L at STP.
Z. When NH3(g) is placed under 10.0 atm pressure at 25 °C, the gas condenses into a liquid.