Which one of the following statements does not describe the equilibrium state?
a. While at equilibrium, a dynamic process is still occurring.  
b. The concentration of the reactants is equal to the concentration of the products.
c. The concentration of the reactants and products reach a constant level.
d. At equilibrium, the net concentration of all species is not changing.
e. All are true.

• A. Choice A
• B. Choice B
• C. Choice C
• D. Choice D
• E. Choice E

Answer: (B)

Verified step by step guidance

1. Understand the concept of chemical equilibrium: At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, meaning the concentrations of reactants and products remain constant over time.
2. Analyze statement A: 'While at equilibrium, a dynamic process is still occurring.' This is true because reactions continue to occur in both directions, but at equal rates, maintaining constant concentrations.
3. Evaluate statement B: 'The concentration of the reactants is equal to the concentration of the products.' This is not necessarily true. At equilibrium, the concentrations are constant but not necessarily equal.
4. Consider statement C: 'The concentration of the reactants and products reach a constant level.' This is true as equilibrium is characterized by constant concentrations.
5. Review statement D: 'At equilibrium, the net concentration of all species is not changing.' This is true because the dynamic balance of forward and reverse reactions keeps concentrations constant.