In the species ${\mathrm{O}}_2,{\mathrm{O}}_2^{+},{\mathrm{O}}_2^{-}\text{and }{\mathrm{O}}_2^{2-}$, the correct decreasing order of bond strength is given as

The formula for calculating bond order:

• $B.O.=\frac{NB-NA}{2}$
• The number of electrons in the antibonding and bonding molecular orbitals, respectively, is NA, NB.

Calculating bond order of given species:

• B.O for ${\mathrm{O}}_2$=1/2×[10–6]; B.O for ${\mathrm{O}}_2$=2
• B.O for ${\mathrm{O}}_2^{-}$-=1/2×[10–7]; B.O for ${\mathrm{O}}_2^{-}$-=1.5
• B.O for ${\mathrm{O}}_2^{+}$=1/2×[10–5]; B.O for ${\mathrm{O}}_2^{+}$=2.5
• B.O for ${\mathrm{O}}_2^{2-}$=1/2×[10–8]; B.O for ${\mathrm{O}}_2^{2-}$=1

Arranging in increasing order of bond length${\mathrm{O}}_2^{+}>{\mathrm{O}}_2>{\mathrm{O}}_2^{-}>{\mathrm{O}}_2^{2-}$