The half-life of a radioactive element is 5 years, then the fraction of the radioactive substance that remains after 20 years is

Answer: Option D

The fraction of a radioactive substance that remains after a certain time period is given by the formula:
Fraction remaining = (1/2)^(time elapsed / half-life)
Given that the half-life of the radioactive element is 5 years and we want to find the fraction remaining after 20 years, we substitute these values into the formula:
Fraction remaining = (1/2)^(20 / 5) = (1/2)^4 = 1/16
So, after 20 years, only 1/16 of the radioactive substance remains.