Question

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?

There are two elements in magnesium phosphate.
There are two molecules of magnesium phosphate.
There are two magnesium ions in a molecule of magnesium phosphate.
There are two phosphate ions in a molecule of magnesium phosphate.

How many atoms of each element are in the chemical formula P2O5?

2 phosphorus and 5 oxygen
5 phosphorus and 2 oxygen
1 phosphorus and 5 oxygen
2 phosphorus and 1 oxygen

Answer 1

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Answer 2

Answer :

Part 1 : The correct statement is, There are two phosphate ions in a molecule of magnesium phosphate.

Part 2 : The correct option is, 2 phosphorus and 5 oxygen

Explanation :

Part 1 :

For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.

The given compound is, $Mg_3(PO_4)_2$

Here, magnesium is having an oxidation state of +2 called as $Mg^{2+}$ cation and phosphate $PO_4^{3-}$ is an anion with oxidation state of -3.

Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral $Mg_3(PO_4)_2$.

From the given formula of compound we conclude that, the subscript 2 means there are two phosphate ions in a molecule of magnesium phosphate and the subscript 3 means there are three magnesium ions in a molecule of magnesium phosphate.

Thus, the correct statement is, There are two phosphate ions in a molecule of magnesium phosphate.

Part 2 :

The subscript present in the chemical formula represents the number of molecules or atoms of an element.

The given chemical formula is, $P_2O_5$

In this chemical formula, there are 2 atoms of phosphorus and 5 atoms of oxygen.

Hence, the correct option is, 2 phosphorus and 5 oxygen