What happens when $CO_2$ is compressed and expanded at a constant temperature of $30.98 \, ^\circ C$?

Two different gases $A$ and $B$ are filled in separate containers of equal capacity under the same conditions of temperature and pressure. On increasing the pressure slightly,gas $A$ liquefies,but gas $B$ does not liquefy even on applying high pressure until it is cooled. Explain this phenomenon.

According to Andrews isothermals,at what temperature does carbon dioxide gas start to condense at $73 \ atm$ (in $^{\circ} C$)?

Explain the liquefaction of gases with the help of an isothermal graph.

Assertion : At critical temperature,liquid passes into gaseous state imperceptibly and continuously.
Reason : The density of liquid and gaseous phase is equal at critical temperature.

Under what conditions can an ideal gas,which follows the kinetic gas equation,be liquefied?