Mean Free Path, Collision Frequency

Q.

If $C_1$, $C_2$, $C_3$........ represent the speeds of $n_1$, $n_2$, $n_3$........ molecules, then the root mean square speed is.......

1. $⟮\frac{n_1{C_1}^2+n_2{C_2}^2+n_3{C_3}^2+.....}{n_1+n_2+n_3+.....}{⟯}^{\frac{1}{2}}$

2. $\frac{{⟮n_1{C_1}^2+n_2{C_2}^2+n_3{C_3}^2+..⟯}^{\frac{1}{2}}}{n_1+n_2+n_3+.....}$

3. $\frac{{⟮n_1{C_1}^2⟯}^{\frac{1}{2}}}{n_1}+\frac{{⟮n_2{C_2}^2⟯}^{\frac{1}{2}}}{n_2}+\frac{{⟮n_3{C_3}^2⟯}^{\frac{1}{2}}}{n_3}+.....$

4. $⟮\frac{{⟮n_1{C}_1+n_2{C}_2+n_3{C}_3+...⟯}^2}{⟮n_1+n_2+n_3+.....⟯}{⟯}^{\frac{1}{2}}$

Q. Which relation is not true about the mean free path of a gas?

1. It is directly proportional to the temperature at a given density of the gas
2. It is inversely proportional to the pressure at a given temperature for a fixed amount of a gas
3. It is directly proportional to the volume of a fixed amount of a gas
4. It is constant for an ideal gas if the number of gas molecules per litre of volume is fixed