Why oxygen is prepared in laboratory by directly heating POTASSIUM CHLORATE?

I am unable in doing my chemistry h.w.Please make it fast .and give a detailed answer.

Potassium Chlorate (KClO3) is often used in highschool and college laboratories to generate oxygen gas; it is a far cheaper source than a pressurized or cryogenic oxygen tank. Potassium Chlorate will readily decompose if heated in contact with a catalyst, typically manganese (IV) oxide (MnO2). Thus, it may be simply placed in a test tube and heated over a burner. If the test tube is equipped with a one-holed stopper and hose, warm oxygen can be drawn off. The reaction is as follows:

2KClO3(s) → 3O2(g) + 2KCl(s)

This is because:
Potassium chlorate is a compound containing potassium, chlorine and oxygen, with the chemical formula K[ClO3].
oxygen is prepared by heating potassium chlorate
in school i have prepared by heating somthing else
potassium chlorate is heated in the presence of manganese oxide as a catalyst to give oxygen. potassium chlorate sublimes on heating and oxygen is released.
oxygen is prepared in the lab by heating a mixture of KClO3 & MnO2 in the ratio of 3;1. (30 g:10g).
since KClO3 takes more time to liberate O 2, MnO2 is added as a catalyst to speed up the reaction.
( look up a text book for the setting up of the apparatus.)

The O2 mixture is taken in a test tube closed with a one-holed rubber cork. The test tube is fixed to a stand in a slightly slanting position. Through the hole(cork) a delivery tube is fitted , the free end of he delivery tube is passed below a bee -hive shelf (you may be familiar )which is kept in a glass trough filled with water.
Keep 3 gas jars completely filled with water. (with the amount of O2 mixture you are sure to fill in threejars).
Heat the test tube using a burner or a spirit lamp . within afew minutes we ca n observe bubbles of air already in the delivery tube escaping through the open end . allow a few seconds. Then carefully place the gas jar invert ed over the bee hive shelf with out spilling the water.

02 starts collcting in the gas jar by the downward displacement of water. When the water is completely pushed down it means the colourless gas that is collected is 02.Carefully remove the gas jar from the trough by placing a glass lid over the mouth of the jar otherwise the gas will escape v.fast. In the meanwhile repeat the procedure with the other 2 jars. ( it needs some practice.)

To test whether the gas collected is O2 we can do the splinter test. Introduce a burning match stick into the jar by just opening the mouth of the jar the match will burn wih a bright flame. Since O2 is a supporter of combustion.

Other than KClO3 , 02 can be prepared by heating KMnO4 or HgO.
But the O2 liberation will be limited.

2 KClO3+MnO2 __2KCl+ 3O2 + MnO2 (MnO2 - does not undergo any chemical change.)

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