A mixture of potassium chlorate, oxalic acid and sulphuric acid is heated. During the reaction which element undergoes maximum change in the oxidation number?

Options

A. S
B. H
C. Cl
D. C

Answer

To solve the problem of determining which element undergoes the maximum change in oxidation number when a mixture of potassium chlorate, oxalic acid, and sulfuric acid is heated, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The reactants are potassium chlorate (KClO3), oxalic acid (H2C2O4), and sulfuric acid (H2SO4).
- The products formed during the reaction are potassium chloride (KCl), potassium sulfate (K2SO4), carbon dioxide (CO2), and water (H2O).

2. **Write the Ionic Forms**:
- Potassium chlorate dissociates into K⁺ and ClO3⁻.
- Oxalic acid dissociates into H⁺ and C2O4²⁻ (oxalate ion).
- Sulfuric acid dissociates into H⁺ and SO4²⁻.

3. **Determine Oxidation States**:
- For chlorine in ClO3⁻:
\[ \text{Let the oxidation number of Cl be } x. \]
\[ x + 3(-2) = -1 \implies x - 6 = -1 \implies x = +5. \]
- For carbon in C2O4²⁻:
\[ \text{Let the oxidation number of C be } y. \]
\[ 2y + 4(-2) = -2 \implies 2y - 8 = -2 \implies 2y = +6 \implies y = +3. \]
- For carbon in CO2:
\[ z + 2(-2) = 0 \implies z - 4 = 0 \implies z = +4. \]

4. **Calculate Changes in Oxidation States**:
- **Chlorine**: Changes from +5 (in ClO3⁻) to -1 (in KCl).
\[ \text{Change} = +5 - (-1) = +6. \]
- **Carbon**: Each carbon in C2O4²⁻ changes from +3 to +4 in CO2.
\[ \text{Change for one carbon} = +3 \to +4 \implies +1. \]
Since there are two carbons, the total change for carbon is:
\[ 2 \times (+1) = +2. \]

5. **Determine the Maximum Change**:
- The maximum change in oxidation number is from chlorine, which changes by +6.
- The change for carbon is +2.

6. **Conclusion**:
- The element that undergoes the maximum change in oxidation number during the reaction is **Chlorine**.

### Final Answer:
**Chlorine undergoes the maximum change in oxidation number.**