At what point does surface tension vanish?

The number of statements,which are correct with respect to the compression of carbon dioxide from point $(a)$ in the Andrews isotherm from the following is $..........$.
$A.$ Carbon dioxide remains as a gas up to point $(b)$
$B.$ Liquid carbon dioxide appears at point $(c)$
$C.$ Liquid and gaseous carbon dioxide coexist between points $(b)$ and $(c)$
$D.$ As the volume decreases from $(b)$ to $(c)$,the amount of liquid decreases

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

Gases can be liquefied by:

$A$ liquid can exist only,

$A$ real gas cannot be liquefied in which of the following conditions?