The correct stability order of the following diazonium salts is

Solution

Chemistry ma’am · 3 steps

Look at the para group: donors feed the N₂⁺ charge and stabilise it, withdrawers destabilise it.

1. What stabilises it. An aryl diazonium ion is stable because the ring shares its π electrons with the -N⁺≡N group by resonance. A para group that pushes more electrons into the ring spreads the positive charge further and makes the salt more stable. A group that pulls electrons out of the ring leaves the charge more concentrated and makes the salt less stable.

   Salt	Para group	Effect on the ring	Stability
   A	-OCH₃	strong +R donor, outweighs its -I	most stable
   C	-H	reference, no extra push or pull	second
   D	-CN	-R and -I withdrawer	third
   B	-NO₂	strongest -R and -I withdrawer	least stable

2. Nitro versus cyano. Both -NO₂ and -CN withdraw electrons, but -NO₂ withdraws more strongly. So B is less stable than D.
3. So. The order is A > C > D > B, which is option (b).

The idea to keep. For a cation attached to a ring, donors at ortho or para positions stabilise it and withdrawers destabilise it. Rank the donors first, then H, then the withdrawers by strength.

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