A positive ion having just one electron ejects it if a photon of wavelength `228Å` or less is absorbed by it. Identify the ion

Explanation

Given, `lambda = 228 A^@`
`E=(hc)/lambda`
`=(6.63 xx 10^-34 xx 3 xx 10^8)/(228 xx 10^-10)`
`=0.0972 xx 10^-16`
The transition takes place form
`n=1` to `n=2`
Now, `1.6 xx 10^-19 xx 13.6 xx 3/4 xx Z^2`
`=0.0872 xx 10^-16`
`Z^2 = (0.0872 xx 10^-16 xx 4)/(13.6 xx 3 xx 16 xx 10^-19) = 5.3`
`Z=sqrt(5.3) = 2.3`
The ion may be Helium.