The reaction A (l) R(g) is allowed to reach equilibrium conditions in an autoclave. At equilibrium, there are two phases, one a pure liquid phase of A and the other a vapor phase of A, R and S. Initially A alone is present. The number of degrees of freedom are

Answer: Option B.

Explanation:

f = C − ϕ + 2 + number of chemical reactions+ number of constraints

⇒ given number of components = 3

Number of phase = 2, number of independent chemical reactions = 1, number of constraints =1 (initially only A is present)
So, f = 2