At equilibrium the reactant and product concentrations are constant because a change in one direction is balanced by a change in the other as the forward and reverse rates become equal: at equilibrium: rate_twd=rate_rev when a chemical system is at equilibrium, a. he concentrations of the reactants and products have reached constant values. b. the concentrations of the reactants are equal to the concentrations of the products. c. the forward and reverse reactions have stopped. d. the reaction quotient, q, has reached a maximum. e. none of the choices.

a. The concentrations of the reactants and products have reached constant values

Explanation:

The reactions which do not go on completion and in which the reactant forms product and the products goes back to the reactants simultaneously are known as equilibrium reactions.  For a chemical equilibrium reaction, equilibrium state is achieved when the rate of forward reaction becomes equal to rate of the backward reaction.

Equilibrium state is the state when reactants and products are present but the concentrations does not change with time and are constant.

Equilibrium constant is defined as the ratio of concentration of products to the concentration of reactants each raised to the power their stoichiometric ratios. It is expressed as

K is the constant of a certain reaction when it is in equilibrium, while Q is the quotient of activities of products and reactants at any stage other than equilibrium of a reaction.

For a equilibrium reaction,

Thus the correct answer is the concentrations of the reactants and products have reached constant values.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.