please some one explain me the what is the mechanism of resonance effect

In chemistry,
Resonance or Mesomerism is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula. A molecule or ion with such delocalized electrons is represented by several contributing structures (also called Resonance Structures or Canonical Forms).
Example for resonating structure

These all are resonance stabilize structure. In all structure only Pi-Electron is delocalised.

Approved