(2) Potassium chlorate reacts to produce potassium chloride and oxygen, so the answer is 2kcl3mno2. △ 2kcl+3o2 ↑。
(3) After gas production by drainage method, oxygen should be prevented from escaping, and the bottle mouth should be covered under the water. So the answer is: cover the gas container cover with glass under the water.
(4) According to the meaning of the question, solid heating device should be used for methane. A is solid heating reaction, B is solid-liquid reaction, and C is gas and gas, so choose A..