Question: What is the half-life of a radioactive substance if it takes 10 years for half of the substance to decay?

Options:

1. 5 years
2. 10 years
3. 20 years
4. 30 years

Correct Answer: 10 years

Solution:

The half-life is defined as the time required for half of the radioactive substance to decay, which is given as 10 years.