Aqueous iron(II) sulfate, FeSO4, is oxidised by an excess of acidified aqueous potassium manganate(VII). In the resulting solution, the oxidation number of iron has changed to +3. What is the correct name of the iron-containing product formed?

IGCSE Chemistry 0620: Naming Compounds Using Oxidation Numbers

Step 1: Recall how oxidation numbers are used in naming

When an element can have more than one oxidation number in its compounds, a Roman numeral is placed immediately after the element’s name to show its oxidation number in that particular compound, for example iron(II) or iron(III).

Step 2: Apply the given oxidation number

The question states that the oxidation number of iron in the product is $+3$ . This is shown by the Roman numeral (III) placed directly after “iron”.

Step 3: Name the compound

The iron is combined with sulfate ions, so the correct name is iron(III) sulfate.

Step 4: Check against the options

Option A keeps the original oxidation number ( $+2$ ), which is incorrect after oxidation.
Option C places the Roman numeral in the wrong position.
Option D wrongly uses the formula subscript ( $3$ from $\text{Fe}_2(\text{SO}_4)_3$ ) as if it were the oxidation number.
Option B correctly names the product using the oxidation number of $+3$ .

Final answer

The product is iron(III) sulfate, option B.