A radioactive substance has a half-life of 20 days what fraction the original radiation nuclei will remain after 80 days?

A. 1/32
B. 1/16
C. 1/ 8
D. 1/4

Correct Answer:

Option B – 1/16

Explanation

80 days = 4 half-life (i.e 4 x 20 days = 80 days)
But the fraction always left by any radioactive material after 4half lives is (1/2)⁴ = 1/16