A first order reaction is half completed...

A first order reaction is half completed in `45` minutes. How long does it need `99.9%` of the reaction to be completed

A

5 hours

B

7.5 hours

C

10 hours

D

20 hours

Verified by Experts

The correct Answer is:

B

`l= (0.693)/(0.75 hr) = (2.303)/(t) log a/(a- 0.999a)`
`= (2.303)/(t) log 10^3 = 7.5 hr`

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