Assertion : Symbol represents one atom of an element.
Reason : Symbol of barium is B.

Options

A. If both assertion and reason are true and reason is the correct explanation
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Symbol represents one atom of an element." This is true because in chemistry, a symbol is a shorthand notation used to represent a chemical element, and it indeed signifies one atom of that element.

2. **Analyzing the Reason**: The reason given is "Symbol of barium is B." To verify this, we need to look up the correct symbol for barium. The correct symbol for barium is actually "Ba," not "B." The letter "B" represents the element boron.

3. **Conclusion**: Since the assertion is true (the symbol represents one atom of an element), but the reason is false (the symbol of barium is not B), we can conclude that the assertion is correct while the reason is incorrect.

4. **Final Answer**: Therefore, the correct relationship is that the assertion is true, but the reason is false. This corresponds to option 3 in the context of typical assertion-reason questions.