1.

If 10% of a radioactive material decays in 5 days, then the amount of original material left after 20 days is approximately

Answer»

0.6
0.65
0.7
0.75

Solution :As, `t=(2.303)/(lambda) log_(10) (N_(0)/N)`
`rArr t=(2.303)/(lambda) log_(10) ((100)/(90))`
`and 20=(2.303)/(lamda) log_(10) ((100)/(X))`
`rArr 1/4 =(log 100-log 90)/(log 100-log x)=(2-1.9542)/(2-log x)`
`rArr 2-log x=8-7.8168 =0.1832`
`log x=1.8168`
`or x=65.58 approx 65%`


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