A radioactive element has a half-life of 2,000 years. If a sample of this element begins with a mass of 100 grams, how long would you have to waitfor the mass to decrease to 25 grams?
A. 4,000 years
B. 8,000 years
C. 500 years
D. 2,000 years

A = 4000 years

Explanation:

Given data:

Half life = 2000 years

Total mass = 100 g

Mass remain = 25 g

Time taken to reduces to 25 g = ?

Solution:

At time zero = 100 g

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

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

Time taken:

Half life = Time elapsed / number of half lives

2000 years = Time elapsed / 2

Time elapsed = 2000 years × 2

Time elapsed = 4000 years

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