Consider the equilibrium system below.

Upper N upper H subscript 4 upper H upper S (s) double-headed arrow upper N upper H subscript 4 upper C l (g).

If the system is at dynamic equilibrium, which statement is true?
Sublimation of the NH4CI crystals stops.
Solidification of the NH4CI vapors stops.
The rate of sublimation of the NH4CI crystals is equal to the rate of solidification of the NH4CI vapors.
The rate of sublimation of the NH4CI crystals is higher than the rate of solidification of the NH4CI vapors.