Correct Answer - Option 4 : Critical temperature
Gases can be converted to liquids by compressing the gas at a suitable temperature. Gases become more difficult to liquefy as the temperature increases because the kinetic energies of the particles that make up the gas also increase. The critical temperature of a substance is the temperature above which vapor of the substance cannot be liquefied, no matter how much pressure is applied. Critical temperature of some of the common gases is given below
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NH3
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132° C
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O2
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- 119° C
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CO2
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31.2° C
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On the other hand critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature.
