Question on Gaseous State

The answer is  

(b) Low T , High P

Because compression(increasing pressure) is needed to make the gas molecules come closer enough so that the interaction forces b/w them becomes sufficient to condense to liquid.However this is possible only below critical temperature .

And low temperature is favorable because as we decrease the temperature the molecular vibrations decreases( i mean amplitude) finally becoming zero at absolute zero (0 k) making it easier to compress the gas.

Finally remember the basic difference b/w solid, liquid and gaseous states( 'plasma' is out of discussion) of matter is the strength of intermolecular forces holding them together.