Analyzing Assertion (A) and Reason (R)

This question requires evaluating two statements about chemical reduction.

Assertion (A) Analysis

The assertion states that a substance losing oxygen during a reaction is reduced. This is a primary definition of reduction in chemistry, often contrasted with oxidation (loss of oxygen). Therefore, Assertion (A) is true.

Reason (R) Analysis

The reason provides a definition for reduction: "Reduction is defined as the gain of hydrogen or loss of oxygen." This definition accurately encompasses key aspects of reduction processes. Therefore, Reason (R) is also true.

Relationship Between A and R

Reason (R) explicitly mentions "loss of oxygen" as part of the definition of reduction. Assertion (A) describes reduction as occurring when a substance "loses oxygen." Since the definition provided in Reason (R) directly supports and explains the phenomenon described in Assertion (A), Reason (R) serves as the correct explanation for Assertion (A).

Conclusion

Both Assertion (A) and Reason (R) are true statements, and Reason (R) correctly explains Assertion (A).

Therefore, the correct option is: Both A and R are true, and R is the correct explanation of A.