The number of electrons donated from substance(s) getting oxidized to the substance(s) getting reduced in the chemical equaton for the following reaction is:
`Cr_2O_(7)^(2-) + Fe^(2+) + C_2O_(4)^(2-)` `rarr` `Cr^(3+) +Fe^(3+) + CO_2`(Unbalanced)

Options

A. 6
B. 5
C. 3
D. 4

Answer

To determine the number of electrons donated from the substances getting oxidized to those getting reduced in the given reaction, we will follow these steps:

### Step 1: Identify the oxidation states of each element in the reaction.
- **Chromium in Cr₂O₇²⁻**: Let the oxidation state of Cr be \( x \). The equation becomes:
\[ 2x + 7(-2) = -2 \implies 2x - 14 = -2 \implies 2x = 12 \implies x = +6 \]
Thus, the oxidation state of Cr in Cr₂O₇²⁻ is +6.

- **Iron in Fe²⁺**: The oxidation state is +2.

- **Carbon in C₂O₄²⁻**: Let the oxidation state of C be \( y \). The equation becomes:
\[ 2y + 4(-2) = -2 \implies 2y - 8 = -2 \implies 2y = 6 \implies y = +3 \]
Thus, the oxidation state of C in C₂O₄²⁻ is +3.

### Step 2: Determine the changes in oxidation states.
- **Chromium (Cr)**: Changes from +6 in Cr₂O₇²⁻ to +3 in Cr³⁺. This indicates a gain of 3 electrons (reduction).

- **Iron (Fe)**: Changes from +2 in Fe²⁺ to +3 in Fe³⁺. This indicates a loss of 1 electron (oxidation).

- **Carbon (C)**: Changes from +3 in C₂O₄²⁻ to +4 in CO₂. This also indicates a loss of 1 electron (oxidation).

### Step 3: Calculate the total number of electrons lost by the oxidized substances.
- The total number of electrons lost by Fe and C:
- Fe loses 1 electron.
- Each of the 2 carbon atoms in C₂O₄²⁻ loses 1 electron, totaling 2 electrons.

Thus, the total number of electrons lost (oxidized) is:
\[ 1 \text{ (from Fe)} + 2 \text{ (from 2 C)} = 3 \text{ electrons} \]

### Step 4: Balance the reaction.
To balance the reaction, we need to ensure that the number of electrons lost equals the number of electrons gained:
- Cr gains 3 electrons, so we need to balance the electrons lost by Fe and C with the electrons gained by Cr.

### Step 5: Conclusion
The total number of electrons donated from the substances getting oxidized (Fe and C) to the substance getting reduced (Cr) is **3 electrons**.

### Final Answer:
The number of electrons donated is **3**.

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