Oxidation Number

To find the average oxidation number of bromine in Br O , we can assume that oxygen has an oxidation number of (since oxygen is typically in compounds). Let the oxidation number of bromine be . The compound is Br O , so:
There are 3 bromine atoms, each with oxidation number .
There are 8 oxygen atoms, each with oxidation number . The sum of oxidation numbers in the compound must be zero because the compound is neutral. Therefore, we can write the equation: Simplifying:

The correct option is (A) :

In the carbonate ion ( ), we can calculate the sum of the oxidation numbers as follows:
- The oxidation number of oxygen in the carbonate ion is , as oxygen generally has an oxidation state of in compounds.
- Let the oxidation number of carbon be .
- Since the overall charge on the carbonate ion is , we can set up the following equation for the sum of oxidation numbers:
Simplifying this equation: Thus, the oxidation number of carbon is , and the oxidation numbers of the three oxygen atoms are each .
Now, summing these oxidation numbers:
Therefore, the sum of the oxidation numbers of all the atoms in the carbonate ion is .
Thus, the correct answer is , which corresponds to option (C).