Aradioactive element of mass 20.0g was isolated and stored. it was discovered after 40days that 2.5g of the element remained undecayed. calculate the half life of the element.

Half life = 13.3 days

Explanation:

Given data:

Mass of element = 20.0 g

After 40 days a mass left = 2.5 g

Half life of element = ?

Solution:

At time zero = 20.0 g

At first half life = 20.0 g/2 = 10.0 g

At second half life = 10.0/2 = 5.0 g

At third half life = 5.0 g/ 2 = 2.5 g

Half life:

Half life = T elapsed / number of half lives

Half life = 40 days / 3

Half life = 13.3 days

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