Which of the following is true about a system at equilibrium? a the concentration(s) of the reactant(s) is equal to the concentration(s) of the product(s). b no new product molecules are formed. c the concentration(s) of reactant(s) is constant over time. d the rate of the reverse reaction is equal to the rate of the forward reaction and both rates are equal to zero. e none of the above (a-d) is true.

In a system at equilibrium, the concentration of reactants is constant with time.

•When the rates of the forward and reverse reactions are equal, a system is said to be in equilibrium.  

•As the forward and reverse reactions take place at equal rates, in a chemical equilibrium, the concentrations of the reactants and products remain same.

•In a reaction, when there is no further change in the concentration of products and reactants, it can be said that the reaction is in equilibrium.  

Thus, the correct answer is option c.

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c The concentration(s) of reactant(s) is constant over time.  

Step-by-step explanation:

When the reaction A ⇌ B reaches equilibrium, the concentrations of reactants and products are constant over time.

a is wrong, because the concentrations of reactants and products are usually quite different.

b is wrong, because both product and reactant molecules are being formed at equilibrium.

d is wrong. The rates of the forward and reverse reactions are equal, but they are not zero.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).

the answer is c.the valence of the atoms combine .