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 the time required for one-half of the radioactive atoms to disintegrate.
$(III)$ The age of the 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 the correct answer using the codes given below:

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

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