$277.$ Law of corresponding states says that

Two different gases behave similarly, if their reduced properties $($i$.$e$.$ P$,$ V and T$)$ are same

The surface of separation $($i$.$ e$.$ the meniscus$)$ between liquid and vapour phase disappears at the critical temperature

No gas can be liquefied above the critical temperature, howsoever high the pressure may be$.$

The molar heat of energy of gas at constant volume should be nearly constant $($about $3$ calories$)$