For the given question two statements are given - one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these question from codes (i), (ii), (iii) and (iv) as given below:
Assertion (A): In a reaction of copper oxide with hydrogen, hydrogen serves as reducing agent.
Reason (R): A substance that gains oxygen in a chemical reaction is 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-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that in the reaction of copper oxide (CuO) with hydrogen (H2), hydrogen acts as a reducing agent.
- A reducing agent is defined as a substance that donates electrons or reduces another substance by undergoing oxidation itself.

2. **Identifying the Reaction**:
- The reaction can be represented as:
\[ \text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O} \]
- In this reaction, hydrogen (H2) reacts with copper oxide (CuO) to produce copper (Cu) and water (H2O).

3. **Analyzing the Role of Hydrogen**:
- In this reaction, hydrogen is losing electrons and is oxidized to form water (H2O). Therefore, it is indeed acting as a reducing agent because it reduces copper oxide (CuO) to copper (Cu).

4. **Understanding the Reason (R)**:
- The reason states that a substance that gains oxygen in a chemical reaction is a reducing agent.
- This statement is incorrect. A reducing agent is characterized by its ability to lose oxygen or gain hydrogen, not by gaining oxygen.

5. **Conclusion**:
- The assertion (A) is true because hydrogen does serve as a reducing agent in the reaction with copper oxide.
- The reason (R) is false because it incorrectly defines a reducing agent.

### Final Answer:
- The correct answer is: (i) A is true, R is false.