Question

(Can you show work for this question please)

If a 10-gram sample of a radioactive element has been stored for 1 week and 2 days, and now only 1.25 g of the element remains, what is its half-life?

A. 1 day

B. 1 week

C. 3 days

D. 2 days

Answer 1

1 week = 7 days

1 week and 2 days = total 9 days, half-life means for every 1 half-life time 50% of the initial amount decayed and remain 50%

10 g --- after 1st half-life

5 g ------ after 2nd half-life

2.5g------- after 3rd half-life

1.25 g ----- remains

so total 3 half-lives completed in 9 days

x² = 9 ==> x = 3 --- this is half-life

-------------------------------OR----------------------------------

half-life = (elapsed time x log2) / log(beginning amount / ending amount)

half-life = (9 days x 0.3010) / log(10 g / 1.25 g) = 3

-------------------------------------------------------------------------

Answer: C. 3 days

Hope this helped you!

Thank You So Much! Please Rate this answer as you wish.("Thumbs Up")