Question

Which of the following species has lowest ionisation enthalpy?

• A. $O$
• B. $O^{+}$
• C. $O^{-}$
• D. $O^{2-}$

Answer 1

The correct option is D $O^{2-}$

$O^{2-}$ has the lowest ionisation energy, because it has more number of electrons in valence shell which create repulsive force among them.
Therefore it is easier to loose an electron. So, $O^{2-}$ has lowest ionisation enthalpy.