In 1,4 delocalisation due to conjugation between all pairs i.e resonance. In 2, 3 conjugation not present between all pairs.
Answer given is 2
Ok, I think in 4 pentavalent nitrogen will be formed if resonance takes place so it's not possible, could be similar for 1 also. Don't know about 3rd
In compound 1 and 4 the delocalisation of positive charge is happening because of resonance.
In 2 and 3 positive charge and pie bond are not in conjugate they are parpendicular. So there is no resonance.
In 1st and 4th option delocalisation is not possible as oxygen cannot make more than 3 bonds and nitrogen cannot make more than 4 bonds.In 3rd option +ve charge is on bridge head carbon..so it cannot be delocalised.
In 2nd option if we break double bond between carbon and nitrogen then delocalisation is possible.
Yes you are correct.i didn’t get the number bond of oxygen and nitrogen are forming after resonance.