4g of a radioactive material of half-life 10 days is spilled on a laboratory floor. How long would it take to disintegrate 3.5g of the material?
-
A.
1(frac{1}{4}) days -
B.
8(frac{1}{4}) days -
C.
30 days -
D.
80 days
Correct Answer: Option C
Explanation
half-life = 10 days
after 10 days, the 4g of element = 2g remaining with 2g disintegrated
after 10 days, 2g of element = 1g left with 1g disintegrated
hence, after 20 days, 3g of the element has been disintegrated with 1g left.
after 10 days, the 1g of element = 0.5g left with 0.5g disintegrated
after 30 days, we have 0.5g of element left with 3.5g disintegrated.