Question

The correct order of ionisation enthalpy for oxygen atom is :

• A. $I.E_1=I.E_2=I.E_3$
• B. $I.E_1<I.E_2<I.E_3$
• C. $I.E_2<I.E_1<I.E_3$
• D. $I.E_3<I.E_2<I.E_1$

Answer 1

The correct option is B $I.E_1<I.E_2<I.E_3$

Electronic conifiguration of oxygen :

${}_8\left[O\right]:1s^{2}2s^{2}2p^4$

As one electron is removed from the outermost shell, the element acquires positive charge and hence the remaining electrons are much strongly bound.

Therefore, the third ionisation enthalpy is greater than second and the first. The second ionisation enthalpy is higher than first ionisation enthalpy because, it is difficult to remove an electron, from more postively charged ion to less positive charge ion or neutral atom.
Therefore, the correct order of ionisation enthalpy for is :
$I.E_1<I.E_2<I.E_3$