Assertion (A) : Restriction enzymes belongs to class nucleases. Reason (R) : Nucleases are of two kinds : exo and endonucleases. Exonucleases remove nucleotides within the DNA.

Options

A. Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
B. Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
C. Assertion (A) is true but reason (R) is false.
D. Assertion (A) is false but reason (R) is true.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion (A)**: The assertion states that "Restriction enzymes belong to class nucleases." To evaluate this, we need to define what restriction enzymes are. Restriction enzymes, also known as restriction endonucleases, are proteins that cut DNA at specific sequences. Since they cleave nucleic acids, they indeed fall under the category of nucleases.

2. **Understanding the Reason (R)**: The reason states that "Nucleases are of two kinds: exo and endonucleases." This is a correct statement. Nucleases are enzymes that cleave the bonds between nucleotides in nucleic acids, and they can be classified into two types:
- **Exonucleases**: These enzymes remove nucleotides from the ends of a DNA molecule.
- **Endonucleases**: These enzymes cut nucleotides at specific internal sites within a DNA molecule.

3. **Evaluating the Specifics of the Reason**: The reason further claims that "Exonucleases remove nucleotides within the DNA." This part of the statement is incorrect. Exonucleases do not remove nucleotides from within the DNA; they remove nucleotides from the ends of the DNA strand. This is a crucial distinction.

4. **Conclusion**: Based on the analysis:
- The assertion (A) is true because restriction enzymes are indeed nucleases.
- The reason (R) is false because it incorrectly describes the function of exonucleases.

Therefore, the final answer is: Assertion is true, but Reason is false.

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