Question

Why co2 and nh3 can be liquefied easily where as h2 o2 and n2 cannot be liquefied?

Answer 1

These gases cannot be liquefied easily because these are elements found in nature in their natural form but in case of CO2 and NH3 these are compounds of carbon and oxygen and nitrogen and hydrogen respectively i think that's what nakes all of that difference.
Hope that helps you
Thanks

Answer 2

To answer this question, it is very important to have the concept that if the intermolecular force of attraction of a gas is weak then it will be very difficult to liquify the gas.

So, since H2, O2 and N2 have very low or weak force of attraction among their molecules, therefore these gases cannot be liquefied.

And as the molecular force of attraction is high in CO2 and NH3, so they can be liquefied easily.