Out of the first 100 elements the number of elements having electrons in the 3d orbital are

Options

A. 80
B. 10
C. 100
D. 60

Answer

To determine the number of elements out of the first 100 that have electrons in the 3d orbital, we can follow these steps:

### Step 1: Understand Electron Configuration
The electron configuration of an element describes the distribution of electrons in atomic orbitals. The 3d orbital starts to fill after the 4s orbital.

### Step 2: Identify the Filling Order
The order of filling for the orbitals is as follows:
1. 1s
2. 2s
3. 2p
4. 3s
5. 3p
6. 4s
7. 3d (starts filling after 4s)

### Step 3: Determine the Range of Atomic Numbers
- The first 20 elements (atomic numbers 1 to 20) have the following electron configuration:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
- Up to atomic number 20, the 3d orbital is not filled.

### Step 4: Identify Where 3d Filling Begins
- The filling of the 3d orbital begins with atomic number 21, where the electron configuration is:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹
- This means that from atomic number 21 to atomic number 100, all these elements will have electrons in the 3d orbital.

### Step 5: Count the Elements with 3d Electrons
- The elements from atomic number 21 to 100 are:
- 100 - 20 = 80 elements
- Therefore, there are 80 elements that have electrons in the 3d orbital.

### Final Answer
The number of elements having electrons in the 3d orbital out of the first 100 elements is **80**.

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