Question

What is oxidation number of sulphur in $SO_3$?

• A. +3
• B. +4
• C. +6
• D. -3

Hint:

Group 16 elements (like Sulphur) have a maximum possible oxidation state of +6, which corresponds to the total number of valence electrons they possess in their outermost shell.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for the formal oxidation state of the central sulphur atom in a neutral molecule of sulphur trioxide ($SO_3$).

Step 2: Key Formula or Approach:
The algebraic sum of the oxidation numbers of all atoms in a neutral polyatomic molecule must equal exactly zero.
$$\sum (\text{Oxidation states}) = 0$$

Step 3: Detailed Explanation:
Let the oxidation state of the sulphur atom be represented by $x$.
Oxygen typically maintains an oxidation state of -2 in almost all its common oxides.
There are three oxygen atoms in the molecule.
Setting up the equation based on our formula rule:
$$x + 3(-2) = 0$$
$$x - 6 = 0$$
$$x = +6$$
Sulphur utilizes all six of its valence electrons to form bonds with the more electronegative oxygen atoms.

Step 4: Final Answer:
The oxidation number of sulphur is +6, which corresponds to option (c).