The compound magnesium phosphate has the chemical formula Mg3(PO4)2. In this compound, phosphorous and oxygen act together as one charged particle, which is connected to magnesium, the other charged particle.What does the 2 mean in the formula 5Mg3(PO4)2?

The 2 outside the parentheses applies to the entire PO₄ group, so each Mg₃(PO₄)₂ formula unit contains two phosphate ions. The 5 in front means there are five formula units; it does not change what the 2 means. The correct choice is “There are two phosphate ions in a molecule of magnesium phosphate.”

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