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 with electrons in the 3d orbital among the first 100 elements, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Range of Elements**: We are considering the first 100 elements in the periodic table.

2. **Understand Electron Configuration**: The electron configuration of elements indicates how electrons are distributed in atomic orbitals. The 3d orbital starts filling after the 4s orbital.

3. **Determine the Filling Order**:
- The order of filling the orbitals follows the Aufbau principle. The 4s orbital is filled before the 3d orbital.
- The first 20 elements (atomic numbers 1 to 20) fill the 1s, 2s, 2p, 3s, and 3p orbitals, and they do not have any electrons in the 3d orbital.

4. **Identify Elements with Electrons in 3d Orbital**:
- Starting from atomic number 21 (Scandium, Z=21), the 3d orbital begins to fill.
- Therefore, elements from atomic number 21 to 100 will have electrons in the 3d orbital.

5. **Count the Elements**:
- The elements from atomic number 21 to 100 are: 21, 22, 23, ..., 100.
- To find the total number of elements in this range, we calculate:
\[ 100 - 20 = 80 \]
- Thus, there are 80 elements that have electrons in the 3d orbital.

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

---