According to MO theory, number of species/ions from the following...

The bond order of a diatomic species can be calculated using molecular orbital theory as follows,

Bondorder = \dfrac{No . ofBMOelectrons - No . ofABMOelectrons}{2}$</p><p>BMO = bonding molecular orbital</p><p>ABMO = Anti bonding molecular orbital.</p><p>Based on the total number electrons in bond orders are given in the following table.</p><table border="1" cellpadding="1" cellspacing="1" style="width: 200px;"> <tbody> <tr> <td style="text-align: center;">Number of${e}^{-}$</td> <td style="text-align: center;">Bond order</td> </tr> <tr> <td style="text-align: center;">$13$</td> <td style="text-align: center;">$2 . 5$</td> </tr> <tr> <td style="text-align: center;">$14$</td> <td style="text-align: center;">$3$</td> </tr> <tr> <td style="text-align: center;">$15$</td> <td style="text-align: center;">$2 . 5$</td> </tr> <tr> <td style="text-align: center;">$16$</td> <td style="text-align: center;">$2$</td> </tr> </tbody></table><p>${CN}^{-}, {NO}^{+}and{O}_{2}^{2 +} are having 14 electrons each, hence the bond order is 3.