Question

Which statements are correct for CO and $N_2$ according to molecular orbital theory ?
(I) Bond order of CO and $N_2$ are 3 and 3
(II) Bond order of CO and $N_2$ are same
(III) During the formation of $N_2^{+}$ from $N_2$ bond length increases
(IV) During the formation of $C{O}^{+}$ from CO, the bond length decreases.

• A. II, IV, I
• B. I, II, III, IV
• C. I, III
• D. I, II, III

Answer 1

The correct option is B I, II, III, IV

Only first three statements are correct. The fourth statement is incorrect.
(I) Bond order of CO and $N_2$ are 3 and 3. Both CO and nitrogen are isoelectronic and contain 14 electrons each. Hence, they have same bond order. $C\equiv O$ and $N\equiv N$
(II) Bond order of CO and $N_2$ are same as they are isoelectronic and have the same number of bonding and antibonding electrons.
(III) During the formation of $N_2^{+}$ from $N_2$ bond length increases. This is because an electron is removed from pi bonding orbital and the bond order decreases from 3 to 2.5. As the bond order decreases, the bond length increases.
(IV) During the formation of $C{O}^{+}$ from CO, the bond length increases. This is because an electron is removed from pi bonding orbital and the bond order decreases from 3 to 2.5.