How many electrons are present in the valence shell of `P` in `PCl_3` ?

Answer

To determine how many electrons are present in the valence shell of phosphorus (P) in the molecule PCl₃, we can follow these steps:

### Step 1: Identify the Electron Configuration of Phosphorus
Phosphorus (P) has an atomic number of 15. Its electron configuration is:
- 1s² 2s² 2p⁶ 3s² 3p³

### Step 2: Determine the Valence Shell Electrons
The valence shell of phosphorus is the third shell (n=3), which includes:
- 3s² (2 electrons)
- 3p³ (3 electrons)

Adding these together gives:
- Total valence electrons = 2 (from 3s) + 3 (from 3p) = 5 valence electrons.

### Step 3: Analyze the PCl₃ Molecule
In PCl₃, phosphorus is the central atom bonded to three chlorine atoms. Each chlorine atom forms a covalent bond with phosphorus.

### Step 4: Count the Electrons in Bonds and Lone Pairs
When phosphorus forms three covalent bonds with chlorine, it uses three of its valence electrons. However, phosphorus also retains one lone pair of electrons.

### Step 5: Total Valence Electrons in PCl₃
Thus, in the valence shell of phosphorus in PCl₃:
- 3 electrons are involved in bonding with chlorine.
- 2 electrons remain as a lone pair.

So, the total number of electrons in the valence shell of phosphorus in PCl₃ is:
- 3 (bonding) + 2 (lone pair) = 5 electrons.

### Conclusion
The number of electrons present in the valence shell of phosphorus in PCl₃ is **5**.

---