1.

A nucleus of Ux_1 has a half life of 24.1 days. How long a sample of Ux_1 will take to change to 90% of Ux_2.

Answer»

80 DAYS
40 days
20 days
10 days

Solution :Here, `lambda=0.693/(T_(1//2)) =0.693/24.1=0.02876 "DAY"^(-1)`
`N=N_0-90%` of `N_0 = N_0/10`
As N=`N_0e^(-lambdat)`
`therefore N_0/10=N_0e^(-lambdat)` or `1/10 = e^(-lambdat)` or `10=e^(lambdat)`
or `log_e10= lambdat`
`therefore t=1/lambda_"log"_e 10=(2.303 log 10)/0.02870 = (2.303xx1)/0.02876 `= 80 days


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