With the help of an experiment show that oxygen is necessary for burning of a candle.

Now cover the burning candle by putting an inverted gas tumbler over it. After a short time, the candle stops burning and gets extinguished.

When the burning candle is covered with a gas jar, the candle takes away the oxygen necessary for burning from the air enclosed in the gas jar. After some time, when all the oxygen of air inside the gas jar is used up, then the burning candle gets extinguished. This proves that oxygen is necessary for the burning of the candle