Assertion (A): In a reaction between copper and oxygen, copper act as a reducing agent.
Reason (R): The compound which gains oxygen in a chemical reaction serves as a reducing agent.

Options

A. Both A and R are true, and R is correct explanation of the assertion.
B. Both A and R are true, but R is not the correct explanation of the assertion.
C. A is true, but R is false.
D. A is false, but R is true.

Explanation

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step 1: Understand the Assertion (A)
The assertion states that in a reaction between copper and oxygen, copper acts as a reducing agent.

- **Chemical Reaction**: The reaction between copper (Cu) and oxygen (O2) can be represented as follows:
\[ 2Cu + O_2 \rightarrow 2CuO \]
- In this reaction, copper reacts with oxygen to form copper(II) oxide (CuO).

### Step 2: Determine the Oxidation States
Next, we need to determine the oxidation states of copper and oxygen in the reaction:

- **Before the Reaction**:
- Copper (Cu) has an oxidation state of 0.
- Oxygen (O2) has an oxidation state of 0.

- **After the Reaction**:
- In CuO, copper has an oxidation state of +2 and oxygen has an oxidation state of -2.

### Step 3: Identify Oxidation and Reduction
Now we analyze what happens to the oxidation states:

- **Copper (Cu)**: Changes from 0 to +2 (oxidation).
- **Oxygen (O)**: Changes from 0 to -2 (reduction).

### Step 4: Define Reducing and Oxidizing Agents
- A **reducing agent** is a substance that donates electrons and is oxidized in the process. In this case, copper is oxidized (loses electrons).
- An **oxidizing agent** is a substance that accepts electrons and is reduced. Here, oxygen is reduced (gains electrons).

### Step 5: Conclusion on Assertion (A)
Since copper is oxidized and causes the reduction of oxygen, it acts as a reducing agent. Therefore, the assertion (A) is correct.

### Step 6: Understand the Reason (R)
The reason states that the compound which gains oxygen in a chemical reaction serves as a reducing agent.

- This statement is misleading. The compound that gains oxygen is typically the oxidizing agent, not the reducing agent. In our reaction, oxygen is the one that gains electrons (is reduced), while copper is the reducing agent.

### Step 7: Conclusion on Reason (R)
Since the reason (R) incorrectly describes the role of the compound gaining oxygen, it is not correct.

### Final Evaluation
- **Assertion (A)**: Correct
- **Reason (R)**: Incorrect

### Answer
The correct answer is that the assertion is true, but the reason is false.

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