Question

A sample of rock is found to contain 100 grams of a parent isotope. How many grams of the parent isotope will remain after two half-lives?
Answer







50








100








75








25

Answer 1

After first half life: 100/2 = 50 grams is left
After second half life: 50/2 = 25 grams is left.

Answer 2

Answer:

Option D - 25

Step-by-step explanation:

Given : A sample of rock is found to contain 100 grams of a parent isotope.

To find : How many grams of the parent isotope will remain after two half-lives.

Solution : A sample of rocks contain parent isotope  = 100 gram

After one half life of the parent isotope i.e. divided by 2

$\frac{100}{2}=50$

After two half lives of the parent isotope means again divide one-half life by 2

 $\frac{50}{2}=25$

Which means 25 gram of the parent isotope will remain after two half lives.

Therefore, Option D is correct -25