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In a mixture of `H- He^(+)` gas (`He+ `is singly ionized He atom), `H` atom and `He+` ions are excited to their respective first sxcited state subequendy `H` atoms transfer their total excilation energy to `He+` ions (by collsions) Assume that the bohr model of atom is exactly veld. The questum number `n` of the state fnally populand in `He^(+)` inos is -A. `2`B. `3`C. `4`D. `5`

Answer» Correct Answer - C
For hydrogen like atom `E_(0) = (-13.6 Z^(2))/(n^(2))eV // atom `
`(for hydrogebn atom)/((Z= 1))` E_(1) = - 13.6 eV`
`E_(2) = -3.4 eV`
:.delta E = E_(2) - E_(1) = - 3.4 - (-13.6 ) = 10.2 eV`
i.e. when hydrogen comes to ground state it will release `10.2 eV` of energy
`(for He^(+)ion)/((Z = 2))` E_(1) = - 13.6 xx 4 eV = - 54.4 eV `
`E_(2) = -13.6eV`
`E_(3) = - 6.04eV`
`E_(4) = - 3.4 eV`
Here `He^(+)` ion is in first excited state i. e. possessing energuy `= 13.6eV` . After receiving of `+ 10.2 eV` from excited hydrogen atom on collsion , the energy of electron will be `(-13.6 + 10.2) eV = -3.4 eV` This means that the electron will jump to `n = 4`


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