Please help with 29.
Answer is 1
You can clearly see that the three nitrogen atoms involved in doubly bonded conjugation, have their lone pairs present and not involved in resonance. So, if any of these gets protonated, its very easy to do so, as the lone pair is just available to grab a proton, and this protonation will not cause any disturbance in the resonance stabilization of the whole molecule.
Thus, 1 should be correct.
Do let me know if you have any doubts.
Can you tell me the reason but How A and e are excluded.(Like if rate asked between a and e
The lone pair of (e) is involved in conjugation, so it will not undergo protonation at the cost of breaking conjugation. In case of (a) also, same thing is happening.