Which variable N represents in the Gibbs phase rule equation?

In the Gibbs phase rule equation, the variable N specifically represents the number of components in a system. Components are the chemically independent constituents of the system; these are the pure substances that can be combined to form the various phases present. The Gibbs phase rule is formulated as:

F = C - P + 2

where F is the degrees of freedom (the number of independent variables that can be changed without affecting the others) for a system at equilibrium, C is the number of components, P is the number of phases, and the "+2" accounts for temperature and pressure.

Therefore, in the context of phase equilibrium, understanding the number of components helps determine how many phases can coexist at equilibrium under varying conditions. The number of components is crucial as it influences the thermodynamic characteristics of the system and the nature of phase transitions.