Assertion `(A) :` The Daniell cell becomes dead after sometimes.
Reason `(R) :` The oxidation protential of `Zn` anode decreases and that of `Cu` increases.

Options

A. If both `(A)` and `(R)` are correct, and `(R)` is the correct explanation of `(A)`.
B. If both `(A)` and `(R)` are correct, but `(R)` is not the correct explanation of `(A)`.
C. If `(A)` is correct, but `(R)` is incorrect.
D. If `(A)` is incorrect, `(R)` is correct.

Answer

To solve the question regarding the assertion and reason related to the Daniell cell, let's break it down step by step.

### Step 1: Understand the Assertion
The assertion states that "The Daniell cell becomes dead after some time."
- The Daniell cell is a type of electrochemical cell that generates electricity through a redox reaction between zinc and copper. Over time, the reactants (zinc and copper ions) get consumed, leading to a decrease in the cell's ability to produce electrical energy.

### Step 2: Understand the Reason
The reason states that "The oxidation potential of Zn anode decreases and that of Cu increases."
- In a Daniell cell, zinc serves as the anode where oxidation occurs (Zn → Zn²⁺ + 2e⁻), and copper serves as the cathode where reduction occurs (Cu²⁺ + 2e⁻ → Cu).
- As the reaction proceeds, the concentration of Zn²⁺ ions increases and the concentration of Cu²⁺ ions decreases. This change affects the oxidation and reduction potentials. If the oxidation potential of zinc decreases, it means zinc is losing its tendency to oxidize, and if the oxidation potential of copper increases, it means copper is losing its tendency to reduce.

### Step 3: Analyze the Relationship Between Assertion and Reason
- The assertion is correct because the Daniell cell does eventually become inactive or "dead" as the reactants are consumed.
- The reason provided is also correct because the changes in oxidation potentials of zinc and copper directly relate to the cell's ability to function. As the potentials change, the cell's electromotive force (emf) decreases, leading to the cell becoming inactive.

### Step 4: Conclusion
Both the assertion and reason are correct, and the reason correctly explains why the assertion is true.

### Final Answer
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.