One mole of A present in a closed vessel undergoes decays as:
`._(Z)A^(m) rarr ._(Z - 4)B^(m - 8) + 2 (._(2)He^(4))`
What will be the volume of helium gas collocted at `STP` afterd 20 days `(t_(1//2) "of" A = 10` days)?

Explanation

`N = N_(0) ((1)/(2))^(n)`
where `N =` remaining mole of `A,n =` number of half lives.
`N = 1 ((1)/(2))^(2) = (1)/(4)` `[T = nt_(1//2) implies n = (T)/(t_(1//2)) = (20)/(10)]`
Number of decayed moles `= 1 - (1)/(4) = (2)/(4)`
Number of moles of helium formed
`= 2 xx` Number of decayed moles of `A`
`= 2 xx (3)/(4) = (3)/(2)`
volume of helium at `STP = (3)/(2) xx 22.4 = 33.6 L`