Answer:
Equilibrium
Explanation:
The condition that exists in the flask is called equilibrium.
An equilibrium is a state when the rate of forward reaction equals the rate of backward reaction. A liquid contained in a stoppered flask exhibits evaporation and condensation. The former involves a change in phase from liquid to gas while the latter involved change from gas to liquid. This process continues until an equilibrium is reached when the rate of evaporation equals the rate of condensation. At this point the level of water in the flask becomes constant.
