Thallium-201 has a half-life 73 hours. If 4.0 mg of thallium-201 disintegrates over a period of 6.0 days and 2 hours, how many milligrams of thallium-201 will remain?

Explanation:

Half-life = 73 hours

Disintegration period = 6 days 2 hours = (6*24) hours + 2 hours

= 144 hours + 2 hours

= 146 hours

No. of Half lives = 146 hours / 73 hours

No. of Half lives = 2

Hence, there are 2 half lives passed in 6 days 2 hours.

Amount of thallium-201 left after first half-life:

= 4.0 mg / 2

= 2.0 mg

Amount of thallium-201 left after second half-life:

= 2.0 mg / 2

= 1.0 mg

Hence, the amount of thallium-201 left after 6.0 days and 2 hours is 1.0 mg.

Hope this helped!