Question

If the ionisation energy of hydrogen is $2.18\times {10}^{-19}$J, the first ionisation energy of $H{e}^{+}$ ion is:

• A. $2.18\times {10}^{-19}$J
• B. $4.36\times {10}^{-19}$J
• C. $8.72\times {10}^{-19}$J
• D. $0.545\times {10}^{-19}$J

Answer 1

The correct option is C $8.72\times {10}^{-19}$J

We know,

$IE=\frac{I{E}_H\times Z^2}{n^2}$

$Z=$ atomic no. (For $He=2$)

$n=$ principal quantam no.

$\therefore$ $I{E}_{H{e}^{+}}=\frac{2.18\times {10}^{-19}\times 2^2}{1^2}$

$=8.72\times {10}^{-19}J$