The atomic number of an element is 18. The number of orbitals containing electron pairs in the valence shell is:

Options

A. 2
B. 4
C. 6
D. 8

Explanation

To solve the question regarding the number of orbitals containing electron pairs in the valence shell of an element with an atomic number of 18, we can follow these steps:

### Step-by-Step Solution:

1. **Determine the Atomic Number**:
The atomic number of the element is given as 18.

2. **Write the Electronic Configuration**:
The electronic configuration for an element with atomic number 18 is:
\[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \]

3. **Identify the Valence Shell**:
The valence shell for this element is the third shell (n=3), which includes the orbitals 3s and 3p.

4. **Count the Electrons in the Valence Shell**:
- In the 3s orbital, there are 2 electrons.
- In the 3p orbital, there are 6 electrons.

5. **Determine the Pairing of Electrons**:
- The 3s orbital can hold a maximum of 2 electrons, and since it has 2 electrons, they are paired.
- The 3p orbital can hold a maximum of 6 electrons, and since it has 6 electrons, they are also paired. The 3p orbital consists of three sub-orbitals (3px, 3py, 3pz), each containing 2 electrons (1 pair in each sub-orbital).

6. **Count the Number of Orbitals with Electron Pairs**:
- The 3s orbital has 1 pair of electrons.
- The 3p orbital has 3 pairs of electrons (one pair in each of the three sub-orbitals).

7. **Total Number of Orbitals with Electron Pairs**:
- Total = 1 (from 3s) + 3 (from 3p) = 4 orbitals.

### Final Answer:
The number of orbitals containing electron pairs in the valence shell is **4**.

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