Consider the van der Waals constants, a and b, for the following gases.
       Gas                     Ar            Ne       Kr     Xe
a/(atm dm⁶ mol^–2)      1.3          0.2      5.1    4.1
b/(10^–2dm³ mol^–1)      3.2          1.7      1.0    5.0
Which gas is expected to have the highest critical temperature?

1.  Xe

2.  Ne

3.  Kr 

4.  Ar 

A pressure cooker reduces cooking time for food because: 

1. Heat is more evenly distributed in the cooking space 

2. Boiling point of water involved in cooking is increased 

3. The higher pressure inside the cooker crushes the food material 

4. Cooking involves chemical changes helped by a rise in temperature 

'a' and 'b' are van der Waals' constants for gases. Chlorine is more easily liquefied than ethane because: