Oxidation Number Calculation for Aluminum in Al2(O2)3

The image shows the chemical formula . This formula is unusual in standard chemistry notation for a stable compound. However, assuming this represents a compound for which we need to determine the oxidation number of aluminum ( ), we must first identify the charge of the polyatomic ion .

The formula is .
In this compound, Aluminum ( ) is almost always present as the cation .
The general rule for ionic compounds is that the total positive charge must balance the total negative charge.
Let the charge of the peroxide-like group be .
The compound structure suggests:

Assuming has its typical oxidation state of :

So, the polyatomic ion in this formula is , which is the peroxide ion.

In the peroxide ion ( ), the total charge is , and there are two oxygen atoms.
Let the oxidation number of a single oxygen atom be .

Since we established that the compound balances the charges with and , the oxidation number of Aluminum ( ) in this hypothetical compound is .

If the problem implicitly intended to ask for the oxidation number of based on the structure , the answer is . If it intended to ask for the oxidation number of , the answer is . Since is the metal and usually has a fixed oxidation state in simple compounds, it is the most likely intended target.

The oxidation number of Aluminum ( ) in is .