Two electrolytic cells, one containing acidified ferrous chloride and another acidified ferric chloride are connected in series. The ratio of iron deposited at cathodes in the two cells will be :

Question

Accepted Answer

To understand why Option 4 (3:2) is the correct answer for the ratio of iron deposited at the cathodes in the two electrolytic cells, we need to consider the electrochemical reactions occurring in each cell and the stoichiometry involved.

### Explanation for Option 4 (3:2):

1. **Electrolytic Cell with Acidified Ferrous Chloride (FeCl₂):**
   - In this cell, the reaction at the cathode involves the reduction of ferrous ions (Fe²⁺) to metallic iron (Fe).
   - The half-reaction is: 
     $$
     \text{Fe}^{2+} + 2e^- \rightarrow \text{Fe}
     $$
   - This indicates that 2 moles of electrons are required to deposit 1 mole of iron.

2. **Electrolytic Cell with Acidified Ferric Chloride (FeCl₃):**
   - In this cell, the reaction at the cathode involves the reduction of ferric ions (Fe³⁺) to metallic iron (Fe).
   - The half-reaction is:
     $$
     \text{Fe}^{3+} + 3e^- \rightarrow \text{Fe}
     $$
   - This indicates that 3 moles of electrons are required to deposit 1 mole of iron.

3. **Cells Connected in Series:**
   - When the cells are connected in series, the same quantity of electricity (same number of moles of electrons) passes through both cells.
   - For every 6 moles of electrons passing through the cells, the ferrous chloride cell will deposit 3 moles of iron (since 2 moles of electrons deposit 1 mole of iron), and the ferric chloride cell will deposit 2 moles of iron (since 3 moles of electrons deposit 1 mole of iron).

4. **Ratio of Iron Deposited:**
   - Therefore, the ratio of iron deposited at the cathodes in the two cells is 3:2.

### Explanation for Why Other Options are Incorrect:

1. **Option 1 (3:1):**
   - This option suggests that the ferrous chloride cell deposits three times as much iron as the ferric chloride cell. However, as calculated, the correct ratio is 3:2, not 3:1.

2. **Option 2 (2:1):**
   - This option implies that the ferrous chloride cell deposits twice as much iron as the ferric chloride cell. The stoichiometry of the reactions shows that the ratio is 3:2, not 2:1.

3. **Option 3 (1:1):**
   - This option suggests equal deposition of iron in both cells. Given the different electron requirements for reduction in each cell, the deposition cannot be equal. The correct ratio is 3:2.

By understanding the stoichiometry of the reactions and the implications of connecting the cells in series, we can confidently conclude that Option 4 (3:2) is the correct answer.