Question

The sum of the oxidation numbers of all the carbon and oxygen atoms in carbonate ion is:

• A. +1
• B. +2
• C. -2
• D. -1
• E. -3

Hint:

In polyatomic ions like carbonate, remember that the sum of the oxidation numbers of all atoms equals the charge on the ion. The oxidation number of oxygen is typically \( -2 \), and the overall charge determines the oxidation number of other elements.

Answer 1

The Correct Option is C

In the carbonate ion (\( {CO}_3^{2-} \)), we can calculate the sum of the oxidation numbers as follows:
- The oxidation number of oxygen in the carbonate ion is \( -2 \), as oxygen generally has an oxidation state of \( -2 \) in compounds.
- Let the oxidation number of carbon be \( x \).
- Since the overall charge on the carbonate ion is \( -2 \), we can set up the following equation for the sum of oxidation numbers:
\[ x + 3(-2) = -2. \] Simplifying this equation: \[ x - 6 = -2 \quad \Rightarrow \quad x = +4. \] Thus, the oxidation number of carbon is \( +4 \), and the oxidation numbers of the three oxygen atoms are each \( -2 \). 
Now, summing these oxidation numbers: \[ +4 + 3(-2) = +4 - 6 = -2. \] 
Therefore, the sum of the oxidation numbers of all the atoms in the carbonate ion is \( -2 \).
Thus, the correct answer is \(-2\), which corresponds to option (C).