Question

A certain radioactive element has a half-life of one hour. if you start with 1.0 gram of the element at noon, how much of the radioactive element will be left at 2 p.m.? 0.50 grams 0.25 grams 0.125 grams 0.0 grams

Answer 1

answer: 0.25 g
I just took this test and that was the answer to it.

Answer 2

The radioactive element will be left at 2 p.m. will be 0.25 g.

Step-by-step explanation:

Half life of the radioactive element =
`t_{(1)/(2)}=1 hour`

Initial concentration of the radioactive element =
`N_o`=1.0 g

Time elapsed = 12:00 pm to 2:00 pm = 2 hours

Concentration of radioactive element left = N

`\lambda =\frac{0.693}{t_{(1)/(2)}}=(0.693)/(1 hr)=0.693 hr^(-1)`

`\log N=\log N_o-(\lambda t)/(2.303)`

Putting the given values in the above equation we get:

N = 0.25 gram

The radioactive element will be left at 2 p.m. will be 0.25 g.