Here's why:

* Chemical equilibrium is not about reactions stopping. It's a dynamic state where the rates of the forward and reverse reactions are equal. This means that reactants are continuously turning into products, and products are continuously turning back into reactants at the same rate.

* The concentrations of reactants and products remain constant at equilibrium. While the reactions don't stop, the net change in the concentrations is zero. This is because the rate of formation of reactants equals the rate of their consumption, and the same holds true for products.

Option a is incorrect because reactions don't stop at equilibrium, they continue at equal rates.

Option c is not a valid description of equilibrium.

Let me know if you have any more questions!