In a reversible reaction, the forward reaction takes place {after, before, simultaneously} the reverse reaction. such a reaction, on reaching equilibrium, will have

In a reversible reaction, the forward reaction takes place simultaneously the reverse reaction. Such a reaction, on reaching equilibrium, will have equal rate of going forward and going backward.

Explanation: It is a reaction in which the reactants reacts to give products and products reacts to give the reactants back simultaneously.

In the above reaction reactants A and B reacts together to give products C and D, and vice versa.

In these reaction rate of reaction going forward is equal the rate of reaction going backward at the equilibrium.