A : Oxidation number of carbon in HCN is +4.
R : Oxidation state and valency is same for carbon.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are false statements, then mark (4).

Answer

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

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the oxidation number of carbon in HCN (hydrogen cyanide) is +4.
- To verify this, we need to determine the oxidation state of carbon in HCN.

2. **Assigning Oxidation States**:
- In HCN, we have:
- Hydrogen (H) typically has an oxidation state of +1.
- Nitrogen (N) typically has an oxidation state of -3.
- Let the oxidation state of carbon (C) be represented as \( x \).

3. **Setting Up the Equation**:
- The sum of oxidation states in a neutral molecule must equal zero. Therefore, we can write the equation:
\[ +1 + x - 3 = 0 \]
- Simplifying this equation gives:
\[ x - 2 = 0 \quad \Rightarrow \quad x = +2 \]
- Thus, the oxidation state of carbon in HCN is +2, not +4.

4. **Conclusion for Assertion (A)**:
- Since the assertion states that the oxidation number of carbon in HCN is +4, and we found it to be +2, the assertion is **false**.

5. **Understanding the Reason (R)**:
- The reason states that the oxidation state and valency are the same for carbon.
- Valency refers to the number of electrons an atom can lose, gain, or share during a chemical reaction. For carbon, the valency is 4 (as it can form four bonds).

6. **Comparing Oxidation State and Valency**:
- We have established that the oxidation state of carbon in HCN is +2.
- Since the valency of carbon is 4 and its oxidation state in this case is +2, they are not the same.

7. **Conclusion for Reason (R)**:
- Therefore, the reason that states oxidation state and valency are the same for carbon is also **false**.

8. **Final Conclusion**:
- Both the assertion (A) and the reason (R) are false.

### Final Answer:
- Both Assertion (A) and Reason (R) are false.