Make up the chemical formulas of the compounds: Potassium oxide, hydrochloric acid, calcium phosphate, barium hydroxide.

Potassium oxide – K2O. It is obtained by the interaction of oxygen and potassium, or by heating potassium nitrate with metallic potassium
Hydrochloric acid – HCl. Obtained by dissolving hydrogen chloride in water
Calcium Phosphate – Ca3 (PO4) 2 (calcium metal salt and phosphoric acid)
Barium hydroxide – Ba (OH) 2. Obtained by reacting metallic barium with water, or barium oxide with water, or barium sulfide with hot water

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