Question

If I now have 3g of Iodine-131, how much did I have 16 days ago?

Answer 1

Answer:

12 grams of Iodine-13 was present 16 days ago

Explanation:

Given:

Amount of  Iodine-131 sample present now  = 3g

To Find:

Amount of Iodine-131 sample present before 16 days = ?

Solution:

W know that the half life of  Iodine-131  is  8days

Let the amount of sample before 16 days be X

Then

The  X amount  Iodine-131 sample will decay ito ist half after 8 days

after 8 days

=> $X \times \frac{1}{2}$

=> $\frac{X}{2}$

after  next 8 days , i.e., 16 days

=> $\frac{X}{2}\times \frac{1}{2}$

=> $\frac{X}{4}$

Now we know that after 16 days we have 3 grams of Iodine-131 sample

So,

$\frac{X}{4}$  = 3

$X = 4 \times 3$

X = 12