Which of the following may be considered to be an organometallic compound?
(a)Ferrocene
(b)cis platin
(c)Zeise's salt
(c)Grignard reagent

Explanation

To determine which of the given options can be considered organometallic compounds, we need to understand the definition of organometallic compounds. Organometallic compounds are characterized by the presence of at least one metal-carbon bond. Let's analyze each option step by step.

### Step 1: Analyze Ferrocene
- **Ferrocene** is composed of iron (Fe) and two cyclopentadienyl (C5H5) anions. The structure can be represented as Fe(C5H5)2.
- There is a direct metal-carbon bond between the iron and the carbon atoms of the cyclopentadienyl ligands.
- **Conclusion**: Ferrocene is an organometallic compound.

### Step 2: Analyze Cisplatin
- **Cisplatin** is a coordination compound with the formula Pt(NH3)2Cl2. It consists of platinum (Pt) bonded to two ammonia (NH3) molecules and two chloride (Cl) ions.
- There are no carbon atoms present in the structure; it only contains metal and non-carbon ligands.
- **Conclusion**: Cisplatin is not an organometallic compound.

### Step 3: Analyze Zeise's Salt
- **Zeise's Salt** is represented as K[PtCl3(C2H4)], where platinum (Pt) is coordinated to three chloride ions and an ethylene (C2H4) molecule.
- There is a metal-carbon bond between platinum and the ethylene molecule.
- **Conclusion**: Zeise's Salt is an organometallic compound.

### Step 4: Analyze Grignard Reagent
- **Grignard Reagent** has the general formula R-MgX, where R is an alkyl or aryl group and X is a halogen.
- There is a metal-carbon bond between the magnesium (Mg) and the carbon of the alkyl or aryl group.
- **Conclusion**: Grignard Reagent is an organometallic compound.

### Final Conclusion
Based on the analysis:
- **Organometallic Compounds**:
- (a) Ferrocene
- (c) Zeise's Salt
- (d) Grignard Reagent
- **Not an Organometallic Compound**:
- (b) Cisplatin

### Summary of Answers
The options that can be considered organometallic compounds are:
- (a) Ferrocene
- (c) Zeise's Salt
- (d) Grignard Reagent