A) 16h
B) 12h
C) 8h
D) 4h
Correct Answer: B
Solution :
We know, \[{{N}_{t}}={{N}_{0}}\times {{\left( \frac{1}{2} \right)}^{n}}\] where\[{{N}_{t}}=\]amount left after expiry of 'n' half lives \[{{N}_{0}}=\]initial amount \[n=\]number of half lives elapsed \[\frac{{{N}_{t}}}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}\] \[\frac{1}{64}={{\left( \frac{1}{2} \right)}^{n}}\] \[{{\left( \frac{1}{2} \right)}^{6}}={{\left( \frac{1}{2} \right)}^{n}}\] \[n=6\] Time taken \[(T)={{t}_{1/2}}\times n=2\times 6=12\,h\]
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