If a reaction is first-order with respect to a particular reactant, when the concentration of that reactant is increased by a factor of 2, the reaction rate will .

It would increase by a factor of 2

Explanation:

The rate law for a fist order reaction is given as;

A --> B

rate = k [A]

upon doubling the concentration, we have;

rate = k [A]

rate 2 = k 2 [A]

Dividing both equations;

rate 2 / rate 1 = k 2 [A] / k [A]

rate 2 / rate 1  = 2 / 1

The ratio between rate 2 and rate 1 is 2 : 1. This means that the reaction rate would also increase by a factor of 2.