So, fill in: emulsification;

(2) plant ash (active ingredient is K2CO3) contains potassium and belongs to potash fertilizer;

Therefore, fill in: potassium;

(3) Steamed bread contains starch, that is, sugar. Roasted ham, chicken soup and spiced dried bean curd are rich in protein, fat, inorganic salts and water, but lack of vitamins. Fruits and vegetables are rich in vitamins.

Therefore, fill in: vitamins;

(4) Iron is more active than copper and easily corroded, so it is more likely to react with other substances in nature, so it is more likely to be corroded;

So iron is easily corroded.