1.

How many atoms of `0.1 g`-atom of a radioacitve isotope `._(Z)X^(A)` (half life = 5 days) will decay during the 11th day?

Answer» `N_(0) = 0.1g` atoms, `t = 10` day and `t_(1//2) = 5` day
`lambda = (2.303)/(t) log_(10) (N_(0))/(N)`
`(0.6963)/(5) = (2.303)/(10) log_(10) (0.1)/(N)`
`:. N_(10)` i.e., amount left after 10 day `0.0250g` atom
Similarly, if `t=11day`
`(0.693)/(5)=(2.303)/(11)log__(10)(0.1)/(N)`
`:. N_(11)` i.e., amount left after 11 day `= 0.0218g` atom
`:.` Amount decayed in `11th` day `= N_(10) - N_(11)`
`= 0.0250-0.0218 = 3.2xx10^(-3)g` atoms
`= 3.2xx6.023xx10^(23) xx 10^(-3)` atoms
`= 1.93xx10^(21)` atoms


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