If a 100 gram sample of a radioactive material with a half-life of 10 years decays for 20 years
will remain
?

25 gram left

Explanation:

Given data:

Total mass = 100 g

Half life of radioactive material = 10 years

Mass left after 20 years = ?

Solution:

First of all we will calculate the number of half lives passed during 20 years.

Number of half lives = time elapsed / half life

Number of half lives = 20 years / 10 years

Number of half lives = 2

At time zero 100 g present.

At first half life = 100 g/2 = 50 g

At 2nd half life = 50 g/2 = 25 g

Thus, after 20 years 25 gram of radioactive material left.

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