The mean free path ($\mathrm{\lambda }$) of a gas sample is given by:

1. $\lambda =\sqrt{2}\pi {\sigma }^{2}N$                               

2. $\lambda =1/\sqrt{2}\pi {\sigma }^{2}N$

3. $\lambda =\sqrt{2}\pi \mu {\sigma }^{2}N$                               

4. none of these

Which is lighter than dry air?

1. Moist air                             

2. SO₂

3. Cl₂                                      

4. O₂

The ratio a/b (the terms used in van der Waals' equation) has the unit-

1. atm litre mol^-1                           

2. atm dm³ mol^-1

3. dyne cm mol^-1                           

4. All of the above

At relatively high pressure, van der Waals' equation reduces to-

1. PV = RT

2. PV = RT + a/v

3. PV = RT + Pb

4. PV = RT - a/V²

The maximum deviation from ideal gas behaviour takes place -  

1. At high temperature and low pressure.

2. At low temperature and high pressure.

3. At high temperature and high pressure.

4. At low temperature and low pressure.

Joule-Thomson coefficient ($\partial \mathrm{T}/\partial \mathrm{P}$)_H for an ideal gas is:

1. zero                                 

2. +ve

3. -ve                                   

4. none of these

All the three states H₂O, i.e., the triple point for H₂O the equilibrium,

                       Ice $\rightleftharpoons$Water$\rightleftharpoons$Vapour exist at:

1. 3.85 mm and 0.0981 $°$C

2. 4.58 mm and 0.0098 $°$C

3. 760 mm and 0$°$C

4. none of the above

The unit of van der Waals' constant 'a' is:

1. atm litre² mol-²                       

2. dyne cm⁴ mol^-2

3. newton m⁴ mol^-2                     

4. All of the above           

The unit of van der Waals' constant 'b' is :

1. cm³ mol^-1

2. litre mol^-1

3. m³ mol^-1

4. All of these 

At STP, 0.50-mole H₂ gas and 1.0 mole He gas                                  

1. have equal average kinetic energies

2. have equal molecular speeds

3. occupy equal volumes

4. have equal effusion rates