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The half life of a radioactive substance is 10 years and its initial mass is 1 g. The remaining amount after 20 years is ________. 

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  1. 0.75 g
  2. 1.00 g
  3. 0.50 g
  4. 0.25 g

Answer (Detailed Solution Below)

Option 4 : 0.25 g
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Detailed Solution

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Given:

Half life =10 years

Initial mass =1g

Time T=20 years

Concept:

Half-life: Half-life is the time period after which half of the quantity of the radioactive element gets decayed. 

The fraction of substance remains after n half-lives is given as,

where  is initial mass.

Explanation:

Put all given values in above formula, we get,

Hence, the correct answer is Option-4-0.25g.

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