Activity of radioactive element decreased to one third of original activity ${R_0}$ in $9$ years. After further $9$ years, its activity will be

  • A

    ${R_0}$

  • B

    $\frac{2}{3}{R_0}$

  • C

    ${R_0}/9$

  • D

    ${R_0}/6$

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column $I$ column $II$
$(A.)$Nuclear fusion $(P.)$ Absorption of thermal neutrons by ${ }_{92}^{213} U$
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