The radioisotope radon-222 has a half life of 3.8 days. How much of a 10 gram sample of radon-222 would be left after 15.2 days?

0.625 g

Explanation:

Given dа ta:

Half life of radon-222 = 3.8 days

Total mass of sample = 10 g

Mass left after 15.2 days = ?

Solution:

Number of half lives = T elapsed / Half life

Number of half lives = 15.2 / 3.8

Number of half lives = 4

At time zero = 10 g

At first half life = 10 g/2 = 5 g

At 2nd half life = 5 g / 2 = 2.5 g

At third half life = 2.5 g/2 = 1.25 g

At 4th half life = 1.25 g/2 = 0.625 g