Xiaohua brought back a bag of crude salt from Hainan. After studying chemistry, he knew that crude salt contained insoluble substances such as sediment and a small amount of soluble impurities. He wanted to be the same. I. The steps of removing insoluble impurities in crude salt are: dissolving, filtering and evaporating;

Ⅱ. Sodium hydroxide solution can react with magnesium chloride to generate white magnesium hydroxide precipitate; Therefore, sodium hydroxide solution was added to the supernatant after the experiment in step 1 to produce white precipitate, which indicated that the crude salt contained magnesium chloride.

Conclusion and Reflection (1) Magnesium carbonate is slightly soluble in water, and white precipitation also occurs; Therefore, the experiment in the first step 1 can't conclude that the conjecture ① holds;

(2) Barium carbonate precipitate can react with hydrochloric acid to generate barium chloride, water and carbon dioxide;

Answer: Ⅰ. Evaporation;

Ⅱ. Sodium hydroxide solution

Conclusion and Reflection (1) Magnesium carbonate is slightly soluble in water;

（2）BaCO3+2HCl=BaCl2+H2O+CO2↑