The starting amount of radioactive iodine-131 was 250 g. The half-life is 8 days. When Leslie measured the amount, she measured 15.625 g of radioactive iodine. How many days have elapsed between measurements

32 days

Explanation:

Half life is the amount of time it takes to get to half of the starting concentration / amount.

Starting amount = 250 g

Half life = 8 days

Amount left = 15.625 g

How many days ? That is, how many half lives

After first Half life;

Amount left = 250 / 2 = 125 g

After second half life;

Amount left = 125 / 2 = 62.5 g

After third half life;

Amount left = 62.5 / 2 = 31.25 g

After fourth half life;

Amount left = 31.25 g / 2 = 15.625 g

That is the radioactive iodine - 131 went though four half lives.

How many days = Number of half lives * Half life

How many days = 4 * 8 = 32 days

for points guys

explanation: it gains negative electrons, therefore becoming negatively charged. as charge cannot be created, nor destroyed, only transferred, this leaves the wool positive. now that they have opposite charges, the two items attract.