EAN of Cr in `[Cr (NH_3)_6] CI_3` is

Options

A. 32
B. 33
C. 34
D. 35

Answer

To find the Effective Atomic Number (EAN) of chromium in the complex ion \([Cr(NH_3)_6]Cl_3\), we can follow these steps:

### Step 1: Identify the Atomic Number of Chromium
The atomic number (Z) of chromium (Cr) is 24.

### Step 2: Determine the Charge on the Central Atom
In the complex \([Cr(NH_3)_6]Cl_3\), the ammonia (NH3) ligands are neutral, while the three chloride (Cl) ions contribute a charge of -3. Therefore, the charge on the chromium ion can be calculated as follows:
- The overall charge of the complex is neutral.
- The charge from the three chloride ions is -3.
- Thus, the charge on chromium (C) is +3.

### Step 3: Calculate the Number of Electrons Accepted from Ligands
Ammonia (NH3) is a neutral ligand and donates 2 electrons per ligand. Since there are 6 ammonia ligands, the total number of electrons accepted from the ligands (E) is:
\[ E = 6 \text{ (ligands)} \times 2 \text{ (electrons per ligand)} = 12 \text{ electrons} \]

### Step 4: Calculate the Effective Atomic Number (EAN)
The formula for EAN is given by:
\[ \text{EAN} = Z + C + E \]
Substituting the values we found:
- \( Z = 24 \)
- \( C = +3 \) (since we consider the charge as positive)
- \( E = 12 \)

Now, substituting these values into the formula:
\[ \text{EAN} = 24 + 3 + 12 \]
\[ \text{EAN} = 39 \]

### Conclusion
The Effective Atomic Number (EAN) of chromium in \([Cr(NH_3)_6]Cl_3\) is 39.