The atomic number of an element is 15. The number of orbitals containing electron pairs in the valence shell is:

Options

A. 1
B. 5
C. 2
D. 3

Answer

To solve the question regarding the number of orbitals containing electron pairs in the valence shell of an element with atomic number 15, we can follow these steps:

### Step 1: Determine the Electronic Configuration
The atomic number of the element is 15. We begin by writing its electronic configuration:
- The first two electrons fill the 1s orbital: 1s²
- The next two electrons fill the 2s orbital: 2s²
- The next six electrons fill the 2p orbital: 2p⁶
- The next two electrons fill the 3s orbital: 3s²
- The last three electrons fill the 3p orbital: 3p³

Thus, the complete electronic configuration is:
1s² 2s² 2p⁶ 3s² 3p³

### Step 2: Identify the Valence Shell
The valence shell for this element is the third shell (n=3), which includes the 3s and 3p orbitals.

### Step 3: Count the Electrons in the Valence Shell
In the valence shell:
- The 3s orbital has 2 electrons (3s²).
- The 3p orbital has 3 electrons (3p³).

### Step 4: Determine the Number of Orbitals with Electron Pairs
An orbital can hold a maximum of 2 electrons. We need to identify which orbitals have paired electrons:
- The 3s orbital has 2 electrons, which means it is a pair (1 pair).
- The 3p orbital has 3 electrons, which means it contains 1 unpaired electron and 1 pair (only 1 orbital can have a pair).

### Conclusion
Thus, the only orbital containing an electron pair in the valence shell is the 3s orbital. Therefore, the number of orbitals containing electron pairs in the valence shell is **1**.

### Final Answer
The number of orbitals containing electron pairs in the valence shell is **1**.

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