The correct answer is D.
The rate of a chemical reaction is proportional to the concentration of the reactants. This means that if the concentration of both the reagents is doubled, the rate of the reaction will also double.
Option A is incorrect because the rate of the reaction will increase, not remain unchanged.
Option B is incorrect because the rate of the reaction will double, not quadruple.
Option C is incorrect because the rate of the reaction will increase, not reduce to one fourth.