Which of the following statements is a true statement concerning a reaction that has reached a state of equilibrium? a. A system has reached equilibrium when there are equal amounts of products and reactants present in the system.
b. A system has reached equilibrium when the rate constant for the forward reaction equals the rate constant of the reverse reaction.
c. A system has reached equilibrium when the reaction has stopped and no more products are formed.
d. A system has reached equilibrium when the concentrations of reactants and products remain constant.

A system has reached equilibrium when the concentrations of reactants and products remain constant.

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.

The equilibrium is dynamic in nature and the reactions are continuous in nature. Rate of forward reaction is equal to the rate of backward reaction.

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

answer is: nuclear fusion produces elements that are heavier than helium.

nuclei combine to form a heavier nucleus, releasing energy.  

for example, fusion of hydrogen atoms at the sun.  

this fusion nuclear reaction is in the inner core of the sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).  

the inner core is the central region of the sun and all solar energy is produced in the core by nuclear fusion.