Half Life — Prelims Questions

A radioactive substance has a half-life of 10 days. If a sample contains $10^6$ nuclei initially, how many nuclei will remain undecayed after 30 days?

The decay constant of a radioactive isotope is $2.31 \times 10^{-4},\text{s}^{-1}$. What is its half-life?

A radioactive sample has an initial activity of $1600,\text{Bq}$. After 2 hours, its activity reduces to $200,\text{Bq}$. What is the half-life of the sample?

Which of the following statements about half-life is INCORRECT?

If the half-life of a radioactive element is 6 hours, what fraction of the original sample will remain after 18 hours?

The mean life of a radioactive sample is 100 seconds. What is its half-life?