A mixture of carbon-dioxide ( $\mathrm{CO}_{2}$ ), nitrogen ( $\mathrm{N}_{2}$ ) and oxygen ( $\mathrm{O}_{2}$ ) are introduced in a rigid and impermeable tank containing only liquid water $\left(\mathrm{H}_{2} \mathrm{O}\right)$. Assume that the components are non-reacting and un-dissociated. The system is kept isolated till an equilibrium is achieved, where only two phases are present. The degrees-of-freedom of the equilibrium mixture, as obtained from the phase rule, is
- $1$
- $2$
- $3$
- $4$
