A) \[1h\]
B) \[0.5\text{ }h\]
C) \[0.25\text{ }h\]
D) \[2\text{ }h\]
Correct Answer: A
Solution :
Kinetics for first order reaction is \[k=\frac{2.303}{t}\log \frac{a}{(a-x)}\] \[\Rightarrow \] \[k=\frac{2.303}{1}\log \frac{0.8}{0.2}\] \[\Rightarrow \] \[k=\frac{2.303}{1}\log 4\] \[\therefore \] \[k=2.303\times 0.6020\] ?..(i) Again, \[\Rightarrow \] \[k=\frac{2.303}{t}\log \frac{0.9}{0.225}\] \[\Rightarrow \] \[k=\frac{2.303}{t}\log 4\] \[\therefore \] \[k=\frac{2.303}{t}\times 0.6020\] ??(ii) From Eqs (i) and (ii) \[\Rightarrow \] \[2.303\times 0.6020=\frac{2.303}{t}\times 0.6020\] \[\therefore \] \[t=1h\]
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