chemistry- equilibrium?

Question

When the chemical reaction
A + B <---> C + D
is at equilibrium,
1. neither the forward nor the reverse reactions have stopped.
2. the forward reaction has stopped.
3. both the forward and reverse reactions have stopped.
4. the sum of the concentrations of A and B equals the sum of the concentrations of C and D.
5. the reverse reaction has stopped.
6. all four concentrations are equal.

Answer 1

1. neither the forward nor the reverse reactions have stopped. Since the consumption rate of A, B, C, or D is the same as the production rate of the same species, the concentration of neither A, nor B, nor C, nor D is changed. This is the DEFINITION of chemistry- equilibrium.
Whatever you will study in the future, please always remember all the DEFINITIONS.