Answered

A radioactive substance has a half-life of 5 million years. What is the age of a rock in which 25% of the original radioactive atoms remain?

Choose one answer.

A2.5 million years
B5 million years
C15 million years
D10 million years

Verified Answer :

Answer:

Hence, the age of rock in which 25% of the original amount remain is:

10 million years.

Step-by-step explanation:

A radioactive substance has a half-life of 5 million years.

What is the age of a rock in which 25% of the original radioactive atoms remain?

Let x be the initial amount of the substance.

Hence, 25% of the initial amount is:

x/4

i.e. in the table form the age could be represented as:

  Years                                      Amount left

5 million years                              x/2      

10 million years                             x/4.

Hence, the age of rock in which 25% of the original amount remain is:

10 million years.

Answer:

d. 10 million years

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