# Which gas can be liquified most readily? a)NH3 b)Cl2 c)SO2 d)CO2 Answer is SO2. I asked this question and expert replied that van der waals force of attraction are strongest in SO2. But how do I know this? Cl2 has the maximum mass then it must also have strong force of attraction?

Dear user,

To which extent a gas can be liquified depends upon its critical temperature and Vander waals forces of attraction.
That is greater the critical temperature, more easily the gas will be liquified.
Below is the critical temperature of these gases :

NH3=406K
Cl2=417K
SO2=430K
CO2=304K

Now, below given is the Vander waals equation :

Liquifaction of gases is directly proportional to 'a'(intermolecular force) which means greater the value of
'a', greater will be liquifaction of gases.That is large value of 'a' coefficients indicates relatively strong
intermolecular force of attraction. And value of 'a' is greater for SO2 gas in comparison to Cl​2 gas
,therefore SO2 will be liquified more easily.
For SO2,
value of a=6.71
For Cl2,
value of a=6.3

From here we can say that SO2 will liquified more easily in comparison to Cl2.

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