Question

The average oxidation state of sulphur in the tetrathionate ion is:

• A. +3
• B. +2.5
• C. +5
• D. +3.5
• E. +1.5

Hint:

Fractional oxidation states often indicate that the element exists in different bonding environments within the same molecule.

Answer 1

The Correct Option is B

To determine the average oxidation state of sulfur in the tetrathionate ion, we must first understand the chemical composition of the tetrathionate ion, which is \(\text{S}_4\text{O}_6^{2-}\).

1. The total charge of the tetrathionate ion is -2.
2. For oxygen, the oxidation state is usually -2.
3. Given the formula \(\text{S}_4\text{O}_6^{2-}\), calculate the total oxidation state of oxygen:
   • Each oxygen has an oxidation state of -2.
   • Thus, for 6 oxygens, the total oxidation state = \(6 \times (-2) = -12\).
4. Let \(x\) be the average oxidation state of sulfur. As there are 4 sulfur atoms, their contribution to the oxidation state will be \(4x\).
5. According to the charge balance equation of the ion: 4x + (-12) = -2
6. Solving the equation:
   • \(4x - 12 = -2\)
   • \(4x = -2 + 12\)
   • \(4x = 10\)
   • \(x = \frac{10}{4} = 2.5\)

Therefore, the average oxidation state of sulfur in the tetrathionate ion is +2.5. This confirms that the correct answer is indeed +2.5, matching with the provided correct answer.