A reaction is of second order with respect to a reactant. How will the rate of reaction be affected if the concentration of this reactant is doubled?

Rate of reaction becomes four times

Since Rate = K[A]²
For second order reaction

Let [A] = a then Rate = Ka²
If [A] = 2a then Rate = K (2a)² = 4 Ka²
∴ Rate of reaction becomes 4 times