Question

A sample of rock contains 80 grams of a parent radioactive isotope that has a half-life of 20 000 years. After 100 000 years, the number of grams of the parent radioactive isotope remaining is

Answer 1

2.5 g

Step-by-step explanation:

Number of half lives is 100000/20000 = 5 half lives

so (1/2)^5 = 1/32 of the original sample remains

So (80)(1/32)=2.5 g