Ionisation energy of `He^+` is `19.6 xx 10^-18 J "atom"^(-1)`. The energy of the first stationary state `(n = 1)` of `Li^( 2 +)` is.

Options

A. `8.82xx010^(-17) J "atom"^(-1)`
B. `4.41xx10^(-16) J "atom"^(-1)`
C. `-4.41xx10^(-17) J "atom"^(-1)`
D. `-2.2xx10^(-15) J "atom"^(-1)`

Answer

C

Explanation

`IE=-E_(1)`
`E_(1) "for" He^(+) "si" =-19.6xx10^(-18) "J mol"^(-1)`
`((E_(1))_(He^(+)))/((E_(1))_(Li^(2+)))=((Z_(He^(+)))^(3))/((Z_(Li^(2+)))^(2))`
`(-19.6xx10^(-18))/((E_(1))_(Li^(2+)))=(4)/(9)`
`E_(1_(Li^(2+)))=((-19.6xx10^(-18))xx9)/(4)`
`=-4.41 "J atom"^(-1)`