The core of an atom contains protons and neutrons.
The bond between the N and 0 (double bond) transfers and gives a -ve charge on O and a +ve charge on N atom at the group . Thus the +vely charged nitrogen is electron-deficient pulling electrons towards itself!
The combination of the +vely charged nitrogen and the electronegative oxygen atom leads to delocalization causing the resonance effect.
Combination or Synthesis Reaction. A combination of synthesis reaction is one. where a new product is synthesized by combination of two or three reactants.
Decomposition Reaction
Displacement or Replacement Reaction
Acid Base Reaction
Combustion Reaction