The number of unpaired electrons in chromium (atomic number 24) is

Options

A. 2
B. 3
C. 5
D. 6

Answer

To determine the number of unpaired electrons in chromium (atomic number 24), we will follow these steps:

### Step 1: Write the Electronic Configuration
The first step is to write the electronic configuration of chromium. The atomic number of chromium is 24, which means it has 24 electrons. The electronic configuration is:

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁴

However, chromium is an exception to the expected filling order due to stability reasons. The correct electronic configuration is:

\[ \text{[Ar]} \, 4s^1 \, 3d^5 \]

### Step 2: Identify the Orbitals and Electrons
In the configuration \(4s^1 \, 3d^5\):
- The \(4s\) subshell has 1 electron.
- The \(3d\) subshell has 5 electrons.

### Step 3: Determine the Number of Unpaired Electrons
Next, we need to determine how many of these electrons are unpaired.

- The \(4s\) subshell has 1 electron, which is unpaired.
- The \(3d\) subshell has 5 electrons. According to Hund's rule, each of the five \(3d\) orbitals will get one electron before any pairing occurs. Therefore, all 5 electrons in the \(3d\) subshell are unpaired.

### Step 4: Calculate the Total Number of Unpaired Electrons
Now, we add the unpaired electrons from both subshells:
- From \(4s^1\): 1 unpaired electron
- From \(3d^5\): 5 unpaired electrons

Total unpaired electrons = 1 (from \(4s\)) + 5 (from \(3d\)) = 6 unpaired electrons.

### Conclusion
The number of unpaired electrons in chromium is **6**.

---