Question

A substance has a half-life of 10,000 years and an initial mass of 1,000 grams. How many years will pass before only 250 grams of the substance's parent material is left?
A. 20,000
B.25,000
C. 30,000
D.40,000

Answer 1

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➷ After 10,000 years the mass will be:

1,000 / 2 = 500

After 20,000 years the mass will be:

500/2 = 250

As you can see, the correct answer would be A. 20,000 years

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Answer 2

Answer:

A). $t = 20,000 years$

Explanation:

Half life is the total time after which the substance will decay and remains only half of the initial amount

So here we will say that

initial amount is 1000 gram

Now after one half life only half of the amount will remain

so it is

$m_1 = 1000/2 = 500 gram$

now again after another half life it will remain half of the initial amount

so it is

$m_2 = 500/2 = 250 gram$

so it took two half lives

$t = 10,000 + 10,000$

$t = 20,000 years$