The formation of the oxide ion, O 2 - ( g ) , from oxygen atom requires first an exothermic and then an endothermic step as shown in below: O g + e - ⟶ O - g ; Δ f H ⊖ = - 141 k J m o l - 1 O - g + e - ⟶ O 2 - g ; Δ f H ⊖ = + 780 k J m o l - 1 Thus process of formation of O 2 - in gas phase is unfavourable though O 2 - is isoelectronic with neon. It is due to the fact that,

Electron repulsion outweighs the stability gained by achieving noble gas configuration.

O - Ion has comparatively smaller size than oxygen atom.

Oxygen is more electronegative.

Addition of electron in oxygen results in larger size of the ion.

EASY

NEET

IMPORTANT

Earn 100

The odd electron molecules among the following is/are:

58.33% studentsanswered this correctly

HARD

NEET

IMPORTANT

In how many of the following species, the central atoms have two lone pairs of electrons?

{XeF}_{4}

{XeF}_{5}^{-}

F_{2} {SeO}_{2}

{XeF}_{3}^{+}

{XeOF}_{4}

{ClOF}_{3}

{ICl}_{4}^{-}

{SCl}_{2}

MEDIUM

NEET

IMPORTANT

Match the species in column (

I

) with their characteristics in column (

II

):

	column $- I$		column $- II$
P	${BH}_{4}^{-}$	$1$	$2$ bond pair and $3$ lone pair on the central atom
Q	${ICl}_{2}^{+}$	$2$	$4$ bond pair and no lone pair on the central atom
R	${ICl}_{2}^{-}$	$3$	$3$ bond pair and 1 lone pair on the central atom
S	${ICl}_{4}^{-}$	$4$	$2$ bond pair and $2$ lone pair on the central atom
		$5$	$4$ bond pair and $2$ lone pair on central atom