The wax on and around the wick melts. Some of the wax boils and gives off a gas which catches fire. This produces heat which melts more wax. This boils and gives off more gas which continues burning. In a lighted candle, it is burning gas which produces the flame.
Chemicals called oxides
Burning substances need to be heated to a certain temperature before they will burn. This temperature is the certain temperature of a burning substance.
A fuel is a material that is used to produce heat and other forms of energy.
E.g. – Wood and Charcoal
Wood is burnt in a special oven called kiln. That oven gets less oxygen than usual. Therefore the wood does not burn completely to leave ash. Instead a black substance is made called, ‘charcoal’.