In transition elements, the last electron enters in the

Options

A. s-orbital of the outermost shell
B. p-orbital of penultimate shell
C. d-orbital of penultimate shell
D. f-orbital of penultimate shell

Explanation

To solve the question regarding where the last electron enters in transition elements, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Transition Elements**: Transition elements are also known as d-block elements. They are characterized by the presence of d orbitals in their electron configuration.

2. **Identify the Electron Configuration**: The general electron configuration for transition elements can be expressed as:
\[ [noble\ gas] \, (n-1)d^{1-10} \, ns^{0-2} \]
Here, \(n\) represents the principal quantum number of the outermost shell, and \(n-1\) represents the penultimate shell.

3. **Determine the Last Electron's Position**: In transition elements, the last electron that is added to the atom enters the d orbital of the penultimate shell (\(n-1\)). This means that for transition elements, the last electron does not enter the outermost s orbital until the d orbitals are filled.

4. **Define Penultimate Shell**: The term "penultimate" refers to the second last shell in the electron configuration of an atom. In the case of transition elements, the penultimate shell is where the d orbitals are located.

5. **Select the Correct Option**: Given the options:
- Option 1: s orbital of the outermost shell
- Option 2: p orbital of the penultimate shell
- Option 3: d orbital of the penultimate shell
- Option 4: f orbital of the penultimate shell

The correct answer is **Option 3: d orbital of the penultimate shell**.

### Final Answer:
The last electron in transition elements enters the **d orbital of the penultimate shell**.

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