In a reversible chemical reaction at equilibrium, if the concentration of any one of the reactants is doubled, then the equilibrium constant will:
also be doubled
remains the same
The correct option is D remains the same
Equilibrium constants aren't changed if you change the concentrations of things present in the equilibrium. The only thing that changes an equilibrium constant is a change of temperature.
The position of equilibrium is changed if you change the concentration of something present in the mixture. According to Le Chatelier's Principle, the position of equilibrium moves in such a way as to tend to undo the change that you have made.
According to Le Chatelier's Principle, if you increase the concentration of Reactant, for example, the position of equilibrium will move to the right to decrease the concentration of reactant again.