Final answer:
The oxidation number of phosphorus (P) in Mg3P2 is -3, balancing the +2 oxidation state of three magnesium (Mg) atoms.
Step-by-step explanation:
To determine the oxidation number of phosphorus (P) in Mg3P2, we need to recognize that magnesium (Mg) generally has a +2 oxidation state. In the compound Mg3P2, there are three magnesium atoms. Using the rules for assigning oxidation states, we know that the sum of the oxidation states in a neutral compound is zero. Thus if magnesium has an oxidation state of +2, and there are three magnesium atoms, the total positive charge is +6. Since the molecule is neutral, the phosphorus atoms must balance this with a combined charge of -6. As there are two phosphorus atoms, each phosphorus atom must have an oxidation number of -3 to achieve this balance.
The oxidation number of phosphorus (P) in Mg3P2 is -3.