JEE Mains 2 April 2026 shift 1 Chemistry

# Q1 of 25

The correct increasing order of bond length among the following is

Options
A.

O 2 + , O2 , O 2 , O 2 2

B.

 O2+,O2,O22,O2

C.

O22,O2,O2,O2+

D.

O2,O22,O2+,O2

Show Answer
Correct Answer

O 2 + , O2 , O 2 , O 2 2

Solution

To determine the correct increasing order of bond length among the given species (O2+, O2, O2, and O22), we can use Molecular Orbital (MO) theory to calculate the bond order for each species.

The relationship between bond order and bond length is inversely proportional:
Bond Length1Bond Order
This means that a higher bond order corresponds to a shorter bond length, and a lower bond order corresponds to a longer bond length.

Let us first write down the molecular orbital configuration for the oxygen molecule (O2), which has 16 electrons:
σ1s2 σ*1s2 σ2s2 σ*2s2 σ2pz2 (π2px2=π2py2) (π*2px1=π*2py1)

The formula for calculating Bond Order (BO) is:
BO=NbNa2
where Nb is the number of bonding electrons and Na is the number of antibonding electrons.

Now, we calculate the bond order for each given species:

1. For O2+ (15 electrons):
One electron is removed from the antibonding molecular orbital (π*2px or π*2py).
Number of bonding electrons, Nb=10
Number of antibonding electrons, Na=5
Bond Order of O2+=1052=2.5

2. For O2 (16 electrons):
Number of bonding electrons, Nb=10
Number of antibonding electrons, Na=6
Bond Order of O2=1062=2.0

3. For O2 (17 electrons):
One electron is added to the antibonding molecular orbital.
Number of bonding electrons, Nb=10
Number of antibonding electrons, Na=7
Bond Order of O2=1072=1.5

4. For O22 (18 electrons):
Two electrons are added to the antibonding molecular orbitals.
Number of bonding electrons, Nb=10
Number of antibonding electrons, Na=8
Bond Order of O22=1082=1.0

Comparing the calculated bond orders:
O2+ (2.5)>O2 (2.0)>O2 (1.5)>O22 (1.0)

Since bond length is inversely proportional to bond order, the increasing order of bond length is the reverse of the bond order sequence:
O2+<O2<O2<O22

Therefore, the correct increasing order of bond length is:
O2+,O2,O2,O22

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