Question

If first ionisation energy of hydrogen is $E$, then the ionisation energy of ${He}^{+}$ would be:

• A. $E$
• B. $2E$
• C. $0.5E$
• D. $4E$

Answer 1

The correct option is D $4E$

$IE=\frac{E{z}^2}{n^2}=0$

i.e for hydrogen $z=1$

$\therefore I.E=E$

For helium, $z=2$ and for first ionization the value of n=1.

$I.E=E{z}^2=E(2{)}^2=4E$