1.

8g of the radioactive isotope, cesium -137 were collected on February 1 and kept in a sealed tube. On July 1, it was found that only 0.25 g of it remained. So the half-life period of the isotope is

Answer»

37.5 days
30 days
23 days
50 days

Solution :t = Feb 1 to July 1 `= 28 + 31 + 30 + 31 + 30 = 150` days
`lamda = (2.303)/(150) "log" (8)/(0.25) = (2.303)/(150) log 2^(5) = (0.693)/(30) "DAY"^(-1)`
`t_(1//2) = (0.693)/(0.693//30)` = 30 days.


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