DDT was widely used insecticide that has been banned in the United States. If DDT had an initial concentration of 8.75 x 10-5 M, how long will it take for the levels of DDT to reach a concentration of 1.41 x 10-7M (a level safe for mammals)

The question is incomplete, the complete question is shown in the image attached.

0.007 days

Explanation:

We know that the half life of a first order reaction is obtained from;

t1/2 = ln 2/k

so;

k = ln2/t1/2

but t1/2 = 56 days

Hence;

k = ln2/56

k =0.0124 days-1

For first order reaction;

ln[A] = ln[A]o - kt

Let ln[A] = final concentration of DDT

Let ln[A]o = initial concentration of DDT

k = rate constant

t = time taken in days

ln[A] - ln[A]o

t = ln[A] - ln[A]o/-k

t =  1.41 x 10-7 - 8.75 x 10-5/-(0.0124)

t = 0.007 days

that's what i got you can count the number of atoms

it is stable as it is in group 0 which have full outer shells of electrons