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

B) 10.0 g

Step-by-step 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^{(-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^{(-0.693*2)/(1) } = 10.0 g`

Answer 2

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.