Question

A certain radioactive element has a half-life of one hour. If you start with 40.0 grams of the element at noon, how much of the radioactive element will be left at 2 p.m.?

A.) 20.0 grams
B.) 10.0 grams
C.) 5.0 grams
D.) 0.0 grams

Answer 1

If you start with 40.0 grams of the element at noon, 10.0 grams radioactive element will be left at 2 p.m. The correct answer between all the choices given is the second choice or letter B. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.

Answer 2

Answer:

B) 10.0 g

Explanation:

Given data:

Half life of the radioactive element = t1/2 = 1 hr

Initial amount, N0 = 40.0 g

Time for radioactive decay. t = 2 hr (12 noon  to 2 P.M)

Formula:

The radioactive decay is expressed mathematically as:

$N(t) = N(0)e^{\frac{-0.693t}{t1/2} }$

where N(t) is the amount of the element left after time t

Substituting the appropriate vales in the above equation we get:

$N(t) = 40.0 * e^{\frac{-0.693*2}{1} } = 10.0 g$