Question

Which best describes dynamic equilibrium?
There is a difference in concentration on either side of the cell membrane.
There is an uneven distribution of particles inside and outside the cell.
Particles are moving into and out of the cell, but their concentrations remain stable.
A concentration gradient is forcing water out of the cell and particles into the cell.

Answer 1

"Particles are moving into and out of the cell, but their concentrations remain stable."

Dynamic equilibrium means continuous motion with no net change—rates of movement in and out are equal, so concentrations stay constant.