Sulphide ions react with `Na_(2)[Fe(NO)(CN)_(5)]` to form a purple coloured compound `Na_(4)[Fe(CN)_(5)(NOS)]` In the reaction, the oxidation state of iron is:

Options

A. Changes from +2 to +3
B. Changes from +3 to +2
C. Changes from +2 to +4
D. Does not change

Answer

To determine the oxidation state of iron in the reaction between sulfide ions and `Na2[Fe(NO)(CN)5]` to form `Na4[Fe(CN)5(NOS)]`, we will follow these steps:

### Step 1: Analyze the first compound `Na2[Fe(NO)(CN)5]`
- Identify the charges of the components:
- Sodium (Na) has a charge of +1, and there are 2 sodium ions, contributing a total of +2.
- The nitrosyl (NO) group has a charge of +1.
- Each cyanide (CN) group has a charge of -1, and there are 5 cyanide groups, contributing a total of -5.

### Step 2: Set up the equation for the first compound
- Let the oxidation state of iron (Fe) be represented as \( x \).
- The overall charge of the complex ion is -2 (since Na2 contributes +2, and the overall charge must balance to -2).
- The equation can be set up as:
\[ x + 1 + (-1 \times 5) = -2 \]
Simplifying this gives:
\[ x + 1 - 5 = -2 \implies x - 4 = -2 \implies x = +2 \]

### Step 3: Analyze the second compound `Na4[Fe(CN)5(NOS)]`
- Identify the charges of the components:
- Sodium (Na) has a charge of +1, and there are 4 sodium ions, contributing a total of +4.
- Each cyanide (CN) group has a charge of -1, and there are 5 cyanide groups, contributing a total of -5.
- The nitroso (NOS) group has a charge of -1.

### Step 4: Set up the equation for the second compound
- Let the oxidation state of iron (Fe) again be represented as \( x \).
- The overall charge of the complex ion is -4 (since Na4 contributes +4, and the overall charge must balance to -4).
- The equation can be set up as:
\[ x + (-1 \times 5) + (-1) = -4 \]
Simplifying this gives:
\[ x - 5 - 1 = -4 \implies x - 6 = -4 \implies x = +2 \]

### Step 5: Conclusion
- The oxidation state of iron in both the initial and final compounds is +2. Therefore, the oxidation state of iron does not change during the reaction.

### Final Answer
The oxidation state of iron is +2.

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