Which of the following statements are true regarding radioactivity (I) All radioactive elements decay exponentially with time (II) Half life time of a radioactive element is time required for one half of the radioactive atoms to disintegrate (III) Age of earth can be determined with the help of radioactive dating (IV) Half life time of a radioactive element is 50% of its average life period Select correct answer using the codes given below Codes: [SCRA 1994]

• A.            I and II                                    
• B.            I, III and IV
• C.            I, II and III
• D.            II and III