If a radioactive source has a half life of 2 hours how long will it take for the activity to go from 200 to 25?

It takes 6h to the radioactive source decrease its activity from 200 to 25

Explanation:

The equation that describes the readioactive decay is:

Ln [A] = -kt + Ln [A]₀

Where [A] could be taken as activity of the source after time t, [A]₀ is initial activity and k is decay constant.

Decay constant could be written as:

k = ln2 / Half-life

k = ln 2 / 2h

k = 0.3466h⁻¹

Replacing in decay equation:

Ln [25] = -0.3466h⁻¹t + Ln [200]

-2.0794 = -0.3466h⁻¹t

6h = t

It takes 6h to the radioactive source decrease its activity from 200 to 25

organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.

the answer is d. 74.02