Which of the following statements are true?

(I) All radioactive element decay exponentially with time.

(II) Half-life time of a radioactive element is the time required for one-half of the radioactive atoms to disintegrate.

(III) Age of the earth can be determined by radioactive dating.

(IV) Half-life time of a radioactive element is fifty percent of its average life period. Select the correct answer using the codes given below.