The ionisation energy of `He^(+)` is `19.6xx10^(-18)"J atom"^(-1)` Calculate the energy of first stationary state of `Li^(2+)` ion. 

Explanation

Ionisation energy of hydrogen like species = Energy of electron in first orbit `x-1`. Since ionisation energy of `He^(+)` is `19.6 xx 10^(-18) J`,
energy of electron in first orbit of `He^(+)` is `-19.6 xx 0^(-18) J`.
`(E_(1))/(E_(2))=(Z_(1)^(2))/(Z_(2)^(2)),(E_(He^(+)))/(E_(Li^(2+))),E_(Li^(2+))=-19.6xx10^(-18)xx(9)/(4)=-4.41xx10^(-17)"J atom"^(-1)`