Which of the following is not a consequence of hydrogen bubbles covering the copper plate of a primary cell?

Analysis

The question asks us to identify which of the listed phenomena is not a direct consequence of hydrogen bubbles accumulating on the copper plate (the positive electrode) of a primary cell, such as a Simple Voltaic Cell.

Concept Explanation

In a simple primary cell, chemical reactions produce hydrogen gas at the copper plate. When these bubbles collect on the plate, they create a layer that prevents the electrolyte from making proper contact with the electrode. This process is known as polarization.

1. Polarization (Option D): This is the direct name for the accumulation of hydrogen bubbles on the positive electrode.
2. Increase in internal resistance (Option B): Because the hydrogen gas is an insulator, it increases the internal resistance of the cell, which reduces the current flowing through the circuit.
3. Formation of hydrogen bubbles (Option A): This is the physical event that causes the polarization.
4. Local Action (Option C): This is a completely different defect. Local action occurs due to impurities in the zinc plate (the negative electrode), which cause small local circuits to form, leading to the consumption of the zinc even when the cell is not in use.

Step-by-Step Solution

• Step 1: Identify the effect of hydrogen bubbles. Hydrogen bubbles on the copper plate cause polarization.
• Step 2: Recognize the impact of polarization. Polarization leads to an increase in internal resistance and a drop in the cell's electromotive force (e.m.f.).
• Step 3: Evaluate "Local Action." Local action is specifically caused by impurities in the zinc electrode, not by the accumulation of hydrogen bubbles on the copper plate.
• Step 4: Conclusion. Since local action is a separate defect caused by a different mechanism (impurities in the zinc), it is not a consequence of hydrogen bubbles on the copper plate.

Answer

The correct option is C.

Exam Tip

To remember the difference:

• Polarization happens at the Copper plate (Positive) and is caused by Hydrogen gas.
• Local Action happens at the Zinc plate (Negative) and is caused by Impurities in the zinc.
• Think: Polarization = Positive plate; Local Action = Level of impurities.