Experimental conclusion According to the experimental phenomenon, it is inferred that NaHCO3 will decompose to generate carbon dioxide when heated, while Na2CO3 will not decompose when heated, so the above conjecture is wrong. The chemical equation of limewater turbidity in beaker C is Ca (OH) 2+CO2 ═ CaCO3 ↓+H2O.

Discussion Ⅱ: Because the sodium bicarbonate solution is alkaline, it cannot be inferred that it must be sodium hydroxide according to the red change of phenolphthalein.

According to the solubility of the substance, calcium ions can be used to identify carbonate, so calcium hydroxide solution can be added.

Therefore, the answer is: experimental conclusion carbon dioxide; Mistakes; ca(oh)2+co2═caco3↓+h2o；

Communication and discussion Ⅱ. The aqueous solution of sodium carbonate and sodium hydroxide is alkaline, which can turn phenolphthalein red;

Calcium hydroxide.