Question

A radioactive isotope has a half-life of ten days. How much of a 100-gram sample will be left after 20 days?
A) 12.5 grams
B) 25.0 grams
C) 50.0 grams
D) 100.0 grams

Answer 1

The radioactive isotope is 25.0 grams

Answer 2

Option (b) is correct.

Explanation:

we know that

$N= N_o (\frac{1}{2})^{n}$

No= initial mass of substance

N= present mass of substance

n= number of half life times

n= total time/half life time

n=20/10

n=2

so $N= 100 (\frac{1}{2})^2$

N= 100/4

N=25 grams