A) \[{{R}_{0}}\]
B) \[\frac{2}{3}{{R}_{0}}\]
C) \[\frac{{{R}_{0}}}{9}\]
D) \[\frac{{{R}_{0}}}{6}\]
Correct Answer: C
Solution :
Activity, \[R={{R}_{0}}{{e}^{-\lambda t}}\] \[\frac{{{R}_{0}}}{3}={{R}_{0}}{{e}^{-\lambda \times 9}}\] \[\Rightarrow \] \[{{e}^{-9\lambda }}=\frac{1}{3}\] After further 9 yr \[R=R{{e}^{-\lambda t}}=\frac{{{R}_{0}}}{3}\times {{e}^{-\lambda \times 9}}\] From Eqs. (i) and (ii), we have \[R=\frac{{{R}_{0}}}{9}\]
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