Concept:The position of equilibrium shifts when a reversible reaction is disturbed by changes in concentration, temperature, or pressure.
Explanation:Le Chatelier’s principle states that a system at equilibrium will respond to a disturbance by shifting in the direction that reduces the effect of the change.
Particle size, stirring, and the presence of a catalyst do not change the equilibrium position.
A catalyst speeds up both the forward and reverse reactions equally, so equilibrium is reached faster but remains unchanged.
Only a change in the concentration of the reactants or products actually shifts the equilibrium position to the left or to the right.
Answer:D. change in concentration of the reactants.