3.
a rock sample contains 80g of a potassium-40
(k10) isotope with a half-life of 1.25 billion years.
how much of the potassium-40 isotope will remain
after 2.5 billion years have passed?
a. og
b. 10g
c. 20g
d. 80g

20 g

We are given;

Original mass of K-40 before decay = 80 g

Half life of Potassium-40 = 1.25 billion years

Time taken by the decay = 2.5 billion years

We are required to calculate the mass of K-10 that will remain after 2.5 billion years.

Using the formula;

Remaining mass = Original mass × (1/2)^n

where n is the number of half lives

Number of half lives, n = Time taken ÷ half-life

                                     = 2.5 billion years ÷ 1.25 billion years

                                     = 2

Remaining mass = 80 g × (0.5)^2

                            = 80 g × 0.25      

                            = 20 g

Therefore, the mass of K-40 isotope that will remain after 2.5 billion years is 20 g.

h let me think

just did the assignment and the answer was #1 +2 n