The reaction a → products is first-order in a. if the concentration of a is cut in half, the half-life of the reaction will
a. double.
b. decrease by a factor of 1/2.
c. remain constant.
d. quadruple.
e. decreased by a factor of 1/4.

c. remain constant.

Explanation:

The half life is defined as the time at which the reactant's concentration reduced to half.

The formula for the half life for a first order kinetic reaction is:

Where,

is the half life

k is the rate constant.

As seen from the formula the half life for a first order reaction is independent of the reactant's concentration.

So, it will remain constant on any change of the reactant's concentration.