Assertion : Bacterial photosynthesis occurs by utilizing wavelength longer than `700` nm.
Reason : Here reaction centre is `B-890`.

Options

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

Explanation

To solve the assertion and reason question, we need to analyze both statements carefully.

### Step 1: Analyze the Assertion
The assertion states: "Bacterial photosynthesis occurs by utilizing wavelengths longer than 700 nm."

- Bacterial photosynthesis, particularly in certain types of bacteria (like purple and green sulfur bacteria), does indeed utilize wavelengths in the infrared region, which can be longer than 700 nm. This is true as these bacteria can absorb light in the range of approximately 870 to 1020 nm.

### Step 2: Analyze the Reason
The reason states: "Here the reaction centre is B-890."

- The reaction center referred to as B-890 is indeed a part of the photosynthetic apparatus in some bacteria. It is a type of bacteriochlorophyll that absorbs light in the infrared region. This statement is also true.

### Step 3: Determine the Relationship
Now we need to determine if the reason correctly explains the assertion.

- While both statements are true, the reason does not provide a correct explanation for the assertion. The assertion focuses on the wavelengths used for photosynthesis, while the reason identifies the specific reaction center involved. The presence of B-890 does not directly justify why wavelengths longer than 700 nm are utilized for photosynthesis.

### Conclusion
Based on the analysis:
- Both the assertion and the reason are true.
- However, the reason is not the correct explanation of the assertion.

Thus, the correct answer is: **Both assertion and reason are true, but reason is not the correct explanation of the assertion.**

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