Question

The half-life of uranium-235 is 700 million years. If there are 2000 g of uranium-235 in the original sample, what happens after 2100 million years have passed? Select all that apply.

A.
One half-life has passed.

B.
500 g of the original sample remains.

C.
Two half-lives have passed.

D.
250 g of the original sample remains.

E.
125 g of the original sample remains.

F.
Three half-lives have passed.

Answer 1

Answer:

The correct answer is - D. 250 g of the original sample remains. and F. Three half-lives have passed.

Explanation:

The half-life is the time is required for a quantity to reduce to half of its initial value. In this given case,

The half life cycle - 700 million years

The number of half-life cycle after 21 million years - 21/7

= 3 half life cycles.

Initial amount = 2000 g

after one half-life or 700 million years - 2000/2 = 1000 g

second half-life or 1400 million = 1000/2 = 500 g

third or 2100 million years ago = 500/2 = 250 g.