For a second order reaction, the half-life is equal to:.

Half life = 1 / k[Ao]

Explanation:

From:

1/ [A] = kt + 1/ [Ao]

Isolating t on its own, we have:

kt = 1 / [A] - 1 / [Ao]

t = 1 / [Ao] / k

Re-arranging we have:

t = 1 / k [Ao]

The t represents the t=half life of the second order reaction and the formula can be re-written as:

t1/2 = 1 / k [Ao]

This is so because second order reaction decreases at a much faster rate than zero and first order reactions and there slopes decreases to zero at a much faster rate.

the answer to this question is 3.