Correct Answer: (3) C - P + 2
Solution:The phase rule, first announced by J. Willard Gibbs in 1876, relates the physical state of a mixture to the number of constituents in the system and to its conditions. It was also Gibbs who first called each homogeneous region in a system by the term "phase." When pressure and temperature are the state variables, the rule can be written as follows: F = C - P + 2, where F is the number of independent variables (called degrees of freedom), C is the number of components, and P is the number of state phases in the system.