Which of the following statements are true?
1. All radioactive elements decay exponentially with time.
2. Half-life time of radioactive elements is the time required for one-half of the radioactive atoms to disintegrate.
3. Age of the earth can be determined by radioactive dating.
4. Half-life time of a radioactive element is fifty percent of its average life period.
Select the correct answer:

A. 1 and 3

B. 1, 3 and 4

C. 1, 2 and 3

D. 2 and 3

Answer: Option C