Formula of ferrocene is :

Options

A. `[Fe(CN)_(4)]^(4-)`
B. `[Fe(CN)_(6)]^(3+)`
C. `[Fe(CO)_(5)]`
D. `[Fe(C_(5)H_(5))_(2)]`

Answer

To determine the formula of ferrocene, we can follow these steps:

### Step 1: Understand the Structure of Ferrocene
Ferrocene is a type of coordination compound known as a "sandwich" compound. It consists of two cyclopentadienyl (C5H5) rings that are symmetrically arranged around a central iron (Fe) atom.

**Hint:** Remember that "sandwich" compounds have a central metal atom surrounded by two ligands.

### Step 2: Identify the Ligands
Each cyclopentadienyl ring (C5H5) acts as a ligand. Cyclopentadiene itself has a formula of C5H6, but when it acts as a ligand, it loses a hydrogen atom and carries a negative charge, becoming C5H5⁻.

**Hint:** Ligands can change their formula when they coordinate with a metal, often losing a hydrogen atom.

### Step 3: Determine the Charge on the Iron Atom
In ferrocene, there are two cyclopentadienyl ligands, each with a charge of -1. Therefore, the total negative charge from the two ligands is -2. To balance this, the iron atom must have a +2 charge (Fe²⁺).

**Hint:** The overall charge of the complex must be neutral; balance the charges from the ligands with the charge on the metal.

### Step 4: Write the Formula
Since there are two cyclopentadienyl ligands and one iron atom, we can write the formula for ferrocene as:
\[ \text{Fe(C}_5\text{H}_5\text{)}_2 \]

**Hint:** When writing the formula, remember to indicate the number of ligands by using subscripts.

### Final Answer
The formula of ferrocene is:
\[ \text{Fe(C}_5\text{H}_5\text{)}_2 \]

### Summary of Steps:
1. Understand the structure of ferrocene as a sandwich compound.
2. Identify the ligands (cyclopentadienyl rings).
3. Determine the charge on the iron atom.
4. Write the complete formula based on the number of ligands and the metal.