Assertion : IUPAC name of compound `CH_(3)CH=CH-CHO` is but-2-enal.
Reason : Functional group gets preference over multiple bond in the IUPAC name of a compound.

Options

A. If both assertion and reason are correct and reason is correct explanation for assertion.
B. If both assertion and reason are correct but reason is not correct explanation for assertion.
C. If assertion is correct but reason is incorrect.
D. If both assertion and reason are incorrect.

Explanation

To solve the question, we need to analyze the assertion and reason provided regarding the compound \( CH_3CH=CH-CHO \).

### Step-by-Step Solution:

1. **Identify the Structure of the Compound**:
The given compound is \( CH_3CH=CH-CHO \). It consists of four carbon atoms, with a double bond and an aldehyde functional group.

2. **Determine the Functional Groups**:
- The compound has an aldehyde group (-CHO) at the end of the carbon chain.
- It also has a double bond between the second and third carbon atoms.

3. **Number the Carbon Chain**:
To name the compound according to IUPAC rules, we need to number the carbon chain. The numbering should start from the end of the chain closest to the functional group (aldehyde in this case):
- Starting from the aldehyde carbon, the numbering is as follows:
- C1: \( CHO \) (aldehyde)
- C2: \( CH \) (double bond)
- C3: \( CH \) (double bond)
- C4: \( CH_3 \)

4. **Assign the IUPAC Name**:
- The root name for a four-carbon chain is "but".
- The position of the double bond is at carbon 2, so we add "2-en".
- Since there is an aldehyde functional group at carbon 1, we add the suffix "al".
- Therefore, the IUPAC name is "but-2-enal".

5. **Evaluate the Assertion**:
The assertion states that the IUPAC name of the compound is but-2-enal, which we have confirmed to be true.

6. **Evaluate the Reason**:
The reason states that the functional group gets preference over multiple bonds in the IUPAC naming. This is also true, as the presence of the aldehyde functional group takes precedence over the double bond when determining the numbering and naming of the compound.

7. **Conclusion**:
Since both the assertion and the reason are true, and the reason correctly explains the assertion, we conclude that the assertion is true and the reason is the correct explanation for the assertion.

### Final Answer:
- Both the assertion and reason are true, and the reason is the correct explanation for the assertion.