Acell is in_
when solute concentrations inside and outside the cell are equal.
concentration
equilibrium
solution
diffusion

A cell is in equilibrium  when solute concentrations inside and outside the cell are equal.

Explanation:

The equilibrium is state when the concentration of the system is same both inside and outside. There will be movement in the particles of the solute in which the cell is placed although its a equilibrium state. but the movement will not cause any further changes to the concentration of the solution because there will be  movement of same and equal number of particle in the same direction. A cell in a  human body  cannot be in a equilibrium state because the human body requires a continuous and constant flow of materials into and out of the cell  in order to keeps the metabolic pathways from attaining equilibrium so as to make the cell to do work throughout the life.

this would be a math