`K_(2)Cr_(2)O_(7)+C_(2)O_(4)^(2-)+H_(2)SO_(4)rarr K_(2)SO_(4)+CO_(2)+Cr_(2)(SO_(4))_(3)+H_(2)O`
In above reaction, identify the elements which do not undergo change in their oxidation state `:`

Options

A. `C`
B. `S & C`
C. `K,O,S & H`
D. `C & O`

Answer

To determine the elements that do not undergo a change in their oxidation state in the reaction:

\[ K_2Cr_2O_7 + C_2O_4^{2-} + H_2SO_4 \rightarrow K_2SO_4 + CO_2 + Cr_2(SO_4)_3 + H_2O \]

we will follow these steps:

### Step 1: Identify the oxidation states of each element in the reactants.

1. **Potassium (K)** in \( K_2Cr_2O_7 \):
- Oxidation state = +1 (since it is an alkali metal).

2. **Chromium (Cr)** in \( K_2Cr_2O_7 \):
- Let the oxidation state of Cr be \( x \).
- The equation for the oxidation state is:
\[ 2(+1) + 2x + 7(-2) = 0 \implies 2 + 2x - 14 = 0 \implies 2x = 12 \implies x = +6 \]
- Oxidation state of Cr = +6.

3. **Carbon (C)** in \( C_2O_4^{2-} \):
- Let the oxidation state of C be \( y \).
- The equation for the oxidation state is:
\[ 2y + 4(-2) = -2 \implies 2y - 8 = -2 \implies 2y = 6 \implies y = +3 \]
- Oxidation state of C = +3.

4. **Sulfur (S)** in \( H_2SO_4 \):
- Let the oxidation state of S be \( z \).
- The equation for the oxidation state is:
\[ 2(+1) + z + 4(-2) = 0 \implies 2 + z - 8 = 0 \implies z = +6 \]
- Oxidation state of S = +6.

5. **Oxygen (O)** in all compounds:
- Oxidation state = -2.

### Step 2: Identify the oxidation states of each element in the products.

1. **Potassium (K)** in \( K_2SO_4 \):
- Oxidation state = +1.

2. **Sulfur (S)** in \( Cr_2(SO_4)_3 \):
- Oxidation state = +6 (same as in reactants).

3. **Chromium (Cr)** in \( Cr_2(SO_4)_3 \):
- Let the oxidation state of Cr be \( x \).
- The equation for the oxidation state is:
\[ 2x + 3(+6) + 12(-2) = 0 \implies 2x + 18 - 24 = 0 \implies 2x = 6 \implies x = +3 \]
- Oxidation state of Cr = +3.

4. **Carbon (C)** in \( CO_2 \):
- Oxidation state = +4.

5. **Sulfur (S)** in \( K_2SO_4 \):
- Oxidation state = +6.

6. **Oxygen (O)** in all products:
- Oxidation state = -2.

### Step 3: Compare the oxidation states of each element in reactants and products.

- **Potassium (K)**: +1 (reactants) → +1 (products) → No change.
- **Chromium (Cr)**: +6 (reactants) → +3 (products) → Change.
- **Carbon (C)**: +3 (reactants) → +4 (products) → Change.
- **Sulfur (S)**: +6 (reactants) → +6 (products) → No change.
- **Oxygen (O)**: -2 (reactants) → -2 (products) → No change.
- **Hydrogen (H)** in \( H_2SO_4 \) and \( H_2O \): +1 (reactants) → +1 (products) → No change.

### Conclusion:
The elements that do not undergo a change in their oxidation state are:
- Potassium (K)
- Sulfur (S)
- Oxygen (O)
- Hydrogen (H)

### Final Answer:
**Potassium (K), Sulfur (S), Oxygen (O), and Hydrogen (H) do not undergo a change in their oxidation state.**