Assertion : In Two-Kingdom classification system, bacteria, blue-green algae and fungi were placed under plants.
Reason : These all organisms had cell wall in their cells.

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the 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 in the Two-Kingdom classification system, bacteria, blue-green algae (cyanobacteria), and fungi were classified under plants. This is correct because, in this classification system proposed by Carl Linnaeus, organisms were primarily divided into two groups: plants and animals.

**Hint**: Remember that the Two-Kingdom classification was based on observable characteristics like the presence of a cell wall.

2. **Understanding the Reason**: The reason given is that these organisms (bacteria, blue-green algae, and fungi) all have a cell wall in their cells. This statement is also correct, as bacteria have a cell wall made of peptidoglycan, blue-green algae have a cell wall made of cellulose, and fungi have a cell wall made of chitin.

**Hint**: Consider the composition of cell walls in different organisms to understand why they were grouped together.

3. **Analyzing the Relationship**: The assertion is true, and the reason is also true. However, the reason explains why these organisms were classified under plants based on the presence of a cell wall. This means that the reason supports the assertion.

**Hint**: Think about how the presence of a cell wall was a key criterion for classification in the Two-Kingdom system.

4. **Conclusion**: Since both the assertion and the reason are true, and the reason provides a correct explanation for the assertion, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

**Hint**: Review the options provided in the question to select the one that matches this conclusion.

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