[A]: Enzyme papain splits antibody molecule into two fragments (fab) (fab = fragment antigen binding) each with antigen binding site.
[R]: The products formed by interaction of antibody antigen depend on number of antigenic determinants present on antibody.

1. If both A and R are true and R is the correct explanation of A
2. If both A and R are true but R is not the correct explanation of A
3. If A is true and R is false
4. If both A and R are false

Options

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

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step-by-Step Solution:

1. **Understanding Assertion (A)**:
- The assertion states that "Enzyme papain splits antibody molecule into two fragments (fab) each with antigen binding site."
- In reality, when papain acts on an antibody, it cleaves it into three fragments: two Fab fragments (which contain the antigen-binding sites) and one Fc fragment. Therefore, the assertion is **false**.

2. **Understanding Reason (R)**:
- The reason states that "The products formed by interaction of antibody-antigen depend on the number of antigenic determinants present on antibody."
- The reason discusses the concept of antigenic determinants (epitopes) and how they relate to the antibody's ability to bind to antigens. However, the phrasing is misleading because it suggests that the products formed depend on the number of determinants on the antibody, whereas it is actually the epitopes on the antigen that are recognized by the antibody. Therefore, the reason is also **false**.

3. **Conclusion**:
- Since both the assertion (A) and the reason (R) are false, the correct answer is **Option 4: If both A and R are false**.