Question

A sample of radioactive material has a half-life of 60 minutes. If you start with 200 grams of this material, how much will remain after 180 minutes?

A. 0g
B. 100g
C. 50g
D. 25g

Answer 1

`\huge\boxed{\sf 25g}`

Step-by-step explanation:

Given that,

Half life = 60 minutes

Time span = 180 minutes

Mass = 200 grams

Required:

Remaining amount = ?

Solution:

No. of half lives = Time span / Half life

No. of half lives = 180 / 60

No. of half lives = 3

So, 3 half lives have passed.

Initial amount = 200 g

After 1 half life:

= 200/2

= 100 g

After 2 half lives:

= 100/2

= 50 g

After 3 half lives:

= 50/2

= 25 g

So,

After 3 half lives, 25g of radioactive material has been left.

`\rule[225]{225}{2}`