In order to understand the structure of a flame, light a wax candle and watch its flame. Carefully note the different coloured zones in the flame. Starting from the base of the flame, a flame has three zones. Check the below figure and try to answer the following question

Why the flame in the outermost zone is blue in colour?

Explanation

It is near the base of the flame. Vapourized wax gets oxidised to carbon monoxide and carbon monoxide burns completely with a blue flame in this zone.