Question

The half-life of potassium-40 is approximately 1.25 billion years. An igneous rock is found to contain about 1/4 of it original mass of potassium-40. What is the approximate age of rock?

Answer Choices
A) 0.0625 billion years
B) 1.25 billion years
C) 2.5 billion years
D) 5.0 billion years

Answer 1

The answer is `option (C)`

Explanation:

The half life of `" Potassium"-40` is #t_(1/2)=1.25 " billion years "#

This means that if the original mass is `m_0 g`

Then after `1.25 " billion years "`, the amount remaining is `=1/2m_0`

And

After `2.5 " billion years "`, the amount remaining is `=1/4m_0`