`KMnO_(4)` acts as an oxidising agent in acidic medium. The number of moles of `KMnO_(4)` that will be needed to react with one mole of sulphide ions in acidic solution is

Options

A. `2//5`
B. `3//5`
C. `4//5`
D. `1//5`

Explanation

To determine the number of moles of `KMnO4` needed to react with one mole of sulfide ions (`S^2-`) in acidic solution, we can follow these steps:

### Step 1: Write the balanced redox reaction
In acidic medium, `KMnO4` acts as an oxidizing agent and can oxidize sulfide ions. The balanced reaction can be written as follows:

\[ 2 \text{KMnO}_4 + 5 \text{S}^{2-} + 8 \text{H}^+ \rightarrow 2 \text{Mn}^{2+} + 5 \text{S} + 4 \text{H}_2\text{O} \]

### Step 2: Identify oxidation states
In this reaction:
- Manganese in `KMnO4` is in the +7 oxidation state and gets reduced to +2 oxidation state.
- Sulfide ions (`S^2-`) are oxidized to elemental sulfur (`S`), where sulfur has an oxidation state of 0.

### Step 3: Determine electron transfer
From the balanced equation:
- Each `KMnO4` molecule accepts 5 electrons (as Mn goes from +7 to +2).
- Each `S^2-` ion loses 2 electrons (as S goes from -2 to 0).

### Step 4: Calculate the mole ratio
From the balanced equation, we see:
- 2 moles of `KMnO4` are required to react with 5 moles of `S^2-`.

### Step 5: Find moles of `KMnO4` needed for 1 mole of `S^2-`
To find out how many moles of `KMnO4` are needed for 1 mole of `S^2-`, we can set up a proportion based on the mole ratio from the balanced equation:

\[ \frac{2 \text{ moles of } KMnO4}{5 \text{ moles of } S^{2-}} = \frac{x \text{ moles of } KMnO4}{1 \text{ mole of } S^{2-}} \]

Cross-multiplying gives:

\[ x = \frac{2}{5} \text{ moles of } KMnO4 \]

### Conclusion
Thus, the number of moles of `KMnO4` needed to react with 1 mole of sulfide ions in acidic solution is:

\[ \frac{2}{5} \text{ moles of } KMnO4 \]

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