Assertion :- O.N. of carbon in `H-C-=N` is `+4`.
Reason :- Carbon always shows an O.N of +4.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False.

Answer

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

### Step 1: Analyze the Assertion
The assertion states that the oxidation number (O.N.) of carbon in the compound H-C≡N (hydrogen cyanide) is +4.

1. **Identify the oxidation states of other elements:**
- Hydrogen (H) typically has an oxidation number of +1.
- Nitrogen (N) in this case, being part of a triple bond with carbon, will have an oxidation number of -3.

2. **Set up the equation:**
- Let the oxidation number of carbon be represented as \( x \).
- The overall charge of the molecule is 0, so we can write the equation:
\[ 1 \times (+1) + 1 \times (x) + 1 \times (-3) = 0 \]

3. **Simplify the equation:**
\[ +1 + x - 3 = 0 \]
\[ x - 2 = 0 \]
\[ x = +2 \]

Thus, the oxidation number of carbon in H-C≡N is +2, not +4. Therefore, the assertion is **false**.

### Step 2: Analyze the Reason
The reason states that carbon always shows an oxidation number of +4.

1. **Understand carbon's oxidation states:**
- Carbon can exhibit multiple oxidation states, ranging from -4 to +4.
- For example, in methane (CH₄), carbon has an oxidation state of -4, and in carbon dioxide (CO₂), it has an oxidation state of +4.

2. **Conclusion about the reason:**
- Since carbon can have oxidation states other than +4, the statement that carbon always shows an oxidation number of +4 is also **false**.

### Final Conclusion
Both the assertion and the reason are false. Therefore, the correct answer is that both statements are incorrect.

### Summary of the Solution
- The assertion is false because the oxidation number of carbon in H-C≡N is +2, not +4.
- The reason is false because carbon does not always have an oxidation number of +4; it can vary between -4 and +4.