A container has two chambers of volumes $V_1=2\text{litres}$ and $V_2=3\text{litres}$ separated by a partition made of a thermal insulator. The chambers contains $n_1=5$ and $n_2=4$ moles of ideal gas at pressures $p_1=1\text{atm}$ and $p_2=2\text{atm}$, respectively. When the partition is removed, the mixture attains an equilibrium pressure of:

1. A
   $1.3\text{atm}$
2. B
   $1.6\text{atm}$
3. C
   $1.4\text{atm}$
4. D
   $1.8\text{atm}$