When Xiao Liang is doing a small family experiment, he wants to explore what he has learned from the data: when baking cakes, household baking powder (mainly composed of sodium bicarbonate) is broken down into (1) Because NaHCO3 decomposes to generate water, there should be water droplets on the inverted beaker. But beaker A buckled the alcohol lamp, while beaker B buckled only the reactants. Therefore, the temperature in beaker A is high, and the water vapor generated by the reaction will not condense into small water droplets. However, the temperature of beaker B is low, and the water vapor generated by the reaction will form small water droplets when it meets the inner wall of the cold beaker.

(2) The method to prove that there is CO2 gas in the beaker is to use clarified limewater for inspection. Therefore, after a period of reaction, the beaker in device B was inverted, and a small amount of clear lime water was added to observe the phenomenon. If limewater becomes turbid, it is proved that CO2 gas exists.

(3) Because the decomposition of sodium bicarbonate will produce carbon dioxide, which neither burns nor supports combustion, carbon dioxide can be used to extinguish the fire, which is also the main extinguishing principle of dry powder fire extinguishers.

(4) If a small amount of NaHCO3 is mixed in Na2CO3, it can be decomposed into Na2CO3, CO2 and water by heating. After CO2 and water vapor escape, only Na2CO3 remains, but Na2CO3 will not be decomposed by heating, so it can be removed by direct heating.

Therefore, the answer is: (1)B, water droplet generation;

(2) Invert the beaker, add a small amount of clarified limewater, oscillate and observe the phenomenon;

(3) When sodium bicarbonate is heated, it decomposes to produce a large amount of CO2, which can put out the fire;

(4) heating.