Question

Which one of the following has the lowest ionization energy?

• A. $1s^2 2s^22p^6$
• B. $1s^22s^22p^63s^1$
• C. $1s^2 2s^22p^5$
• D. $1s^22s^22p^3$

Answer 1

Answer: (B)

$1s^22s^22p^63s^1$

Answer 2

In the Periodic Table, the minimum ionisation energy is found at alkali metals. Hence sodium (electronic configuration $\left.=1 s^{2} 2 s^{2} 2 p^{6} 3 s^{1}\right)$ has the lowest ionisation energy.
Note : - Ionisation energy is the amount of energy required to remove an electron from the outermost shell an isolated atom.