So describe what happens to a reaction when it reaches chemical equilibrium. Now here for A it says the reaction stops. Remember we said that in a dynamic process the reaction doesn't simply stop. So A could not be an answer.
B reactants form products as fast as products form reactants. This is an answer because remember when we get to chemical equilibrium we have a reversible reaction, meaning the rate of the reverse and the rate of the Ford reaction are equal to one another. So the pace at which reactants or products are being formed is equal. This leads to no net change in the concentrations of either your reactants or your products.
Here the collision frequencies of products and reactants are equal or identical. We never went into this detail, so we don't know for certain that this contributes in the same way that our rates would OK, and because of that we can't say it's a vital answer.
4D rate of forward and rate of reverse reactions are equal to 0. This would only happen if the reaction stopped. And again, since we're at equilibrium into dynamic process so the reaction doesn't stop there, would it be equal to 0? They'd be equal to one another. So out of all the choices given, only option B is the correct answer.
