1.

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

Answer»

5 hours
7.5 hours
10 hours
20 hours

Solution :`K = (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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