Chemistry Q53 – JEE-MAIN 2026

Home Chemistry Chemical BondingQuestion #216

Given below are two statements : **Statement (I) :** The correct sequence of bond lengths in the following species is :

O_{2}^{+} < O_{2} < O_{2}^{-} < O_{2}^{2 -}

**Statement (II) :** The correct sequence of number of unpaired electrons in the following species is :

O_{2} > O_{2}^{+} > O_{2}^{-} > O_{2}^{2 -}

In the light of the above statements, choose the correct answer from the options given below :

Clue 1 of 3: Bond Order and Bond Length Relationship

Recall the relationship between bond order and bond length. A higher bond order corresponds to a stronger and shorter bond.

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Ninja Strategy•Unpaired Electron Check

Quickly recall or determine the number of unpaired electrons. Knowing that both superoxide ( $O_{2}^{-}$ ) and dioxygenyl ( $O_{2}^{+}$ ) have one unpaired electron immediately falsifies Statement II, eliminating two options.

🧠 Full Solution Path

Step 1: Determine Bond Order and Unpaired Electrons using MOT✦ Active

We use Molecular Orbital Theory to find the bond order and number of unpaired electrons for each species. The total number of electrons are: $O_{2}^{+}$ (15), $O_{2}$ (16), $O_{2}^{-}$ (17), and $O_{2}^{2 -}$ (18). The MOT configuration for $O_{2}$ is $(σ 1 s)^{2} (σ^{*} 1 s)^{2} (σ 2 s)^{2} (σ^{*} 2 s)^{2} (σ 2 p_{z})^{2} (π 2 p_{x})^{2} (π 2 p_{y})^{2} (π^{*} 2 p_{x})^{1} (π^{*} 2 p_{y})^{1}$ .

From the configurations, we can calculate the bond order (B.O.) and count the unpaired electrons (U.E.):

O_{2}^{+} : B . O . = \frac{1}{2} (10 - 5) = 2.5, U.E. = 1

O_{2} : B . O . = \frac{1}{2} (10 - 6) = 2.0, U.E. = 2

O_{2}^{-} : B . O . = \frac{1}{2} (10 - 7) = 1.5, U.E. = 1

O_{2}^{2 -} : B . O . = \frac{1}{2} (10 - 8) = 1.0, U.E. = 0

Step 2: Evaluate Statement (I): Bond Lengths○ Expand

Bond length is inversely proportional to bond order. The order of bond orders is $O_{2}^{+} > O_{2} > O_{2}^{-} > O_{2}^{2 -}$ (2.5 > 2.0 > 1.5 > 1.0).

Therefore, the order of bond lengths will be the reverse: $O_{2}^{+} < O_{2} < O_{2}^{-} < O_{2}^{2 -}$ . This matches Statement (I).

Thus, **Statement (I) is true**.

Step 3: Evaluate Statement (II): Unpaired Electrons○ Expand

From Step 1, the number of unpaired electrons are: $O_{2}$ (2), $O_{2}^{+}$ (1), $O_{2}^{-}$ (1), $O_{2}^{2 -}$ (0).

The correct sequence of the number of unpaired electrons is $O_{2} > O_{2}^{+} = O_{2}^{-} > O_{2}^{2 -}$ . Statement (II) claims $O_{2} > O_{2}^{+} > O_{2}^{-} > O_{2}^{2 -}$ , which is incorrect because $O_{2}^{+}$ and $O_{2}^{-}$ have the same number of unpaired electrons.

Thus, **Statement (II) is false**.

Step 4: Conclusion○ Expand

Since Statement I is true and Statement II is false, the correct option is the one that reflects this.

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Chemistry Question 53 – JEE-MAIN 2026

Clue 1 of 3: Bond Order and Bond Length Relationship

🧠 Full Solution Path