The half-life of a certain radioactive element is 800 years. How old is an object if only 12.5% of the radioactive atoms in it remain?

Question

a
6400 years
b
1600 years
c
3200 years

Answer 1

The correct answer is option b) 1600 years.

In a radioactive decay process, the amount of radioactive material decreases by half after each half-life period.

Since the half-life of the radioactive element is 800 years, it means that after 800 years, the amount of radioactive material remaining is 50% of the original amount.

If only 12.5% of the radioactive atoms remain in the object, it means that the amount of radioactive material has gone through three half-life periods (12.5% = 1/2^3).

Therefore, the object is 3 x 800 = 2400 years old.

Since each half-life period is 800 years, the age of the object is 2400 - 800 = 1600 years.

Answer 2

The half-life of a certain radioactive element is 800 years. How old is an object if only 12.5% of the radioactive atoms in it remain?

a
6400 years
b
1600 years
c
3200 years