The bond order and the magnetic characteristics of CN⁻ are :

Solution

Chemistry ma’am · 4 steps

Count the electrons first: CN⁻ has 14, the same as N₂, so it behaves exactly like N₂.

1. Count electrons. Carbon brings 6 electrons and nitrogen brings 7. The negative charge adds 1 more, so CN⁻ has 6 + 7 + 1 = 14 electrons. That is the same count as N₂, so the two are isoelectronic.
2. Fill the orbitals. For 14 electrons or fewer, the π 2p orbitals lie below σ 2p_z. The filling is σ 1s² σ^* 1s² σ 2s² σ^* 2s² π 2pₓ² π 2p_y² σ 2p_z². That puts 10 electrons in bonding orbitals and 4 in antibonding orbitals.

   Bond order = (N_b - Nₐ)/2 = (10 - 4)/2 = 3

3. Check magnetism. Every orbital in this filling holds a full pair, so there are no unpaired electrons. A species with no unpaired electrons is diamagnetic.
4. So. CN⁻ has bond order 3 and is diamagnetic, which is option (c).

The idea to keep. Isoelectronic species share the same MO diagram. CN⁻, CO, NO⁺ and N₂ all have 14 electrons, bond order 3, and no unpaired electrons.

Answer from the NTA final answer key. Solution by PrepWiser.