Radiation coming from transition `n = 2 to n = 1` of hydrogen atoms falls on helium in `n = 1 and n= 2` state what are the possible transition of helium ions as they absorb energy from the radiation?

Answer

A, B, C, D

Explanation

From transitions `n=2` to `n=1`
`E=13.6((1)/(1) - (1)/(4))`
`=13.6 xx 3/4 = 10.2 eV`
Let the transitions possible on He
`n=1` to `2`
`E_1 = 4 xx 13.6 (1-(1)/(4))`
`=40.8eV`
`E_1gtE`, Hence it is not possible
`n=1` to `n=3`
`E_2 =4 xx 13.6(1-(1)/(9))`
`=48.3 eV`
`E_2 gt E`. Hence impossible
Similarly , `n=1` to `n=4`
is also not possible.
`n=2` to `n=3`
`E_3 = 13.6 xx 4((1)/(4)-(1)/(9))`
`=(20 xx 13.6)/(36) = 7.56 eV`
As `E_3 lt E` and `E_4 = E`
Hence E_3 and E_4 can be possible