Astudent has an 80 g sample of a radioactive material that has a half-life of 20 seconds. how much material will he have left after one minute?
a) 40 g
b) 1.33 g
c) 5 g
d) 10 g

= 10 g

Explanation:

Half life is the time taken by a radioactive substance to decay by half of the original mass or initial amount.

Therefore, to get the new mass after decay;

New mass = Original mass × (1/2)^n ; where n is the number of half lives.

n = 60 seconds/20 seconds

  = 3

Therefore;

New mass = 80 g × (1/2)^3

                   = 80 g × 1/8

                   = 10 g