In redox chemistry, what is the oxidation number of sulfur in elemental sulfur represented as the S8 molecule?

Introduction / Context:
This question tests your understanding of oxidation numbers, also called oxidation states, in redox chemistry. Oxidation numbers are bookkeeping numbers that help track the transfer of electrons in chemical reactions. A very important rule is that any element in its pure, elemental form, whether it is monatomic like Na, diatomic like O2, or polyatomic like S8, always has an oxidation number of zero. Recognising this rule is crucial for balancing redox equations and identifying which species are oxidised or reduced in a reaction.

Given Data / Assumptions:
- The substance is elemental sulfur written as S8, a molecule of eight sulfur atoms.
- The question asks for the oxidation number of sulfur in this elemental form.
- No other elements are present in the formula; it is a pure element.
- Standard rules for assigning oxidation numbers in chemistry apply.

Concept / Approach:
One of the first rules taught for oxidation numbers is that any atom in its elemental state has an oxidation number of zero. This rule applies regardless of how many atoms of that element are bonded together in the molecule. For example, H2, N2, O2, P4, and S8 all have oxidation numbers of zero for the atoms in those molecules. Only when the element is combined with different elements in a compound, such as in H2SO4 or Na2S, do the oxidation numbers change according to additional rules about electronegativity and overall charge. Therefore, the correct approach is simply to recognise S8 as elemental sulfur and assign an oxidation number of zero to each sulfur atom.

Step-by-Step Solution:
Step 1: Identify S8 as elemental sulfur, meaning the molecule contains only sulfur atoms and no other elements. Step 2: Recall the rule that the oxidation number of any atom in its elemental form is defined as 0. Step 3: Note that this rule applies to all elements, whether they occur as single atoms (Na), diatomic molecules (Cl2), or polyatomic molecules (P4, S8). Step 4: Since S8 is composed entirely of sulfur atoms in their elemental state, each sulfur atom must have an oxidation number of 0. Step 5: Conclude that the oxidation number of sulfur in S8 is 0.

Verification / Alternative check:
You can verify this rule by looking at examples of elemental forms in standard chemistry texts. They consistently list oxidation numbers as 0 for N2, O2, O3, P4, S8, and metallic elements like Fe(s) or Cu(s). When these elements form compounds, such as SO2 or H2SO4, the sulfur atoms acquire nonzero oxidation numbers determined by additional rules. For S8, since there are no other elements to balance and the molecule is overall neutral, assigning oxidation numbers of 0 to each sulfur atom is the only consistent solution. This verification confirms that 0 is correct for sulfur in S8.

Why Other Options Are Wrong:
An oxidation number of +1 or +2 would imply that sulfur in S8 has lost electrons relative to some reference state and that other atoms or charges must be present to balance this, which is not the case for a pure element. An oxidation number of -2 is typical for sulfur in sulfide ions or some compounds like metal sulfides, but not in elemental sulfur. None of these nonzero values satisfy the fundamental rule for elemental substances. Therefore, +1, -2, and +2 are all incorrect answers in this context.

Common Pitfalls:
Students sometimes confuse oxidation numbers in common sulfur compounds, such as -2 in sulfides or +6 in sulfates, with the values in elemental sulfur. Another mistake is to think that the presence of multiple atoms (such as S8) requires a nonzero oxidation state to balance something, when in reality the molecule as a whole is neutral and made of identical atoms. To avoid such errors, always apply the simple rule first: if the species is an element in its standard uncombined form, the oxidation number is 0, regardless of how many atoms make up the molecule.

Final Answer:
The oxidation number of sulfur in elemental S8 is 0.