At which of the following conditions can a gas be liquefied? ($T_c$ and $P_c$ are critical temperature and pressure.)

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.

At what point does surface tension vanish?

At what pressure does $SO_2$ gas liquefy at room temperature?

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.

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