In a voltaic cells, the salt bridge ........

Options

A. is not necessary in order for the cell to work
B. acts as a mechanism to allow mechanical mixing of the solutions
C. allows charge balance to be maintained in the cell
D. is tightly plugged with firm agar gel through
which ions cannot pass

Explanation

**Step-by-Step Solution:**

1. **Understanding the Role of Salt Bridge:**
- In a voltaic cell, the salt bridge is essential for maintaining electrical neutrality. It connects the two half-cells and allows the flow of ions to balance the charges that build up during the electrochemical reactions.

2. **Identifying the Incorrect Options:**
- The first option states that the salt bridge is not necessary for the cell to work. This is incorrect because the salt bridge is crucial for the cell's operation.
- The second option suggests that the salt bridge allows mechanical mixing of solutions. This is also incorrect as the salt bridge does not mix the solutions but allows ion migration.
- The fourth option claims that the salt bridge is tightly plugged with a gel through which ions cannot pass. This is incorrect because the salt bridge allows certain ions to pass through to maintain charge balance.

3. **Correct Option:**
- The correct option is that the salt bridge allows charge balance to be maintained in the voltaic cell. As oxidation occurs at the anode, positive ions accumulate, and as reduction occurs at the cathode, negative ions accumulate. The salt bridge compensates for these changes by allowing ions to move between the two half-cells.

4. **Conclusion:**
- Therefore, the salt bridge is necessary for the functioning of a voltaic cell as it maintains charge balance and allows the cell to continue operating effectively.

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