The activity of a sample of radioactive material is $A_1$ at time $t_1$ and $A_2$ at time $t_2\left(t_2>t_1\right)$ . Its mean life is T. Which of the following is correct?

• A

  $A_1{t}_1=A_2{t}_2$
• B

  $\frac{A_1+A_2}{t_2–t_1}=$ constant
• Correct answer
  C

  $A_2=A_1{e}^{\frac{t_1–t_2}{T}}$
• D

  $A_2=A_1{e}^{\left(\frac{t_1}{T{t}_2}\right)}$

Hence, the correct answer is option: 'C'.