In which zone of the flame fuel remains in vapour form ?

Does yellow flame from a gas burner shows complete burning of the fuel ?

The flame fuel remains in vapour form in the innermost zone of a flame which is dark(or black). As the innermost zone of a flame consists of, unburnt vapours of the combustible material (say, wax vapours).

No, the yellow flame from a gas burner shows a complete burning of a fuel because when the oxygen supply (or air supply) is in sufficient, then the fuel burn incompletely producing mainly a yellow flame.