Question

Oxidation state of iodine in \( I_3^- \) is

• A. \( - (1/3) \)
• B. \( +4 \)
• C. \( +5 \)
• D. \( -3 \)

Hint:

For polyatomic ions of the same element, the average oxidation state is simply the total charge divided by the number of atoms.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
We need the oxidation state of iodine in the triiodide ion \( I_3^- \). This is a polyatomic ion with three iodine atoms and a net charge of \(-1\).

Step 2: Key Formula or Approach:
Let the oxidation state of each iodine atom be \( x \). The sum of oxidation states equals the net charge on the ion.

Step 3: Detailed Explanation:
The algebraic sum: \( 3x = -1 \). Solving: \( x = -\frac{1}{3} \). This is the average oxidation state. In \( I_3^- \), the structure is linear [I–I–I]\(^-\); the central iodine has a formal oxidation state of \(-1\) and the terminal iodines have \( 0 \), but the question asks for the oxidation state of iodine in the ion, which is typically taken as the average.

Step 4: Final Answer:
The oxidation state is \( -\frac{1}{3} \), corresponding to option (A).