Explain:
Easily liquefiable gases have stronger van der waals force of attraction
We know that gases can be liquefied by applying high pressure and lowering the temperature. If there are strong intermolecular forces operating between the particles of a gas, then the gas can be easily liquefied. Thus, easily liquefiable gases have strong vander waal's forces (which are a type of inter-molecular forces) operating between its particles.