A: `[Ni(CO)_(4)]` is organometallic compound.
R: CO is organic and Ni is metal.

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 question, we need to analyze both the assertion (A) and the reason (R) given in the statement.

### Step 1: Understand the Assertion (A)
The assertion states that `[Ni(CO)_(4)]` is an organometallic compound.

- **Definition of Organometallic Compounds**: Organometallic compounds are defined as compounds that contain at least one bond between a carbon atom of an organic molecule and a metal.

- **Structure of `[Ni(CO)_(4)]`**: In nickel tetracarbonyl, nickel (Ni) is the metal and it is bonded to four carbon monoxide (CO) ligands. Each CO ligand has a carbon atom that is directly bonded to the nickel atom.

**Conclusion for Assertion**: Since the carbon atoms in CO are directly bonded to the nickel metal, `[Ni(CO)_(4)]` qualifies as an organometallic compound. Therefore, the assertion is **True**.

### Step 2: Understand the Reason (R)
The reason states that CO is organic and Ni is metal.

- **Nature of CO**: Carbon monoxide (CO) consists of one carbon atom and one oxygen atom. For a compound to be classified as organic, it typically must contain carbon atoms bonded to hydrogen atoms (hydrocarbons). Since CO does not contain hydrogen, it does not meet the criteria for being an organic compound.

- **Nature of Ni**: Nickel (Ni) is indeed a metal, specifically a transition metal known for its hardness and ductility.

**Conclusion for Reason**: The statement that CO is organic is **False** because CO is an inorganic compound. Therefore, while Ni is a metal, the claim about CO being organic is incorrect.

### Final Conclusion
- Assertion (A) is **True**: `[Ni(CO)_(4)]` is an organometallic compound.
- Reason (R) is **False**: CO is not an organic compound.

Thus, the correct answer is that the assertion is true, but the reason is false.