Here's why:

* Phosphorus (P) has 5 valence electrons.

* Chlorine (Cl) has 7 valence electrons.

In PCl3, phosphorus forms three single covalent bonds with three chlorine atoms. Each bond involves the sharing of two electrons, one from phosphorus and one from chlorine.

Here's the breakdown:

* Phosphorus contributes 3 electrons for bonding.

* Chlorine contributes 3 electrons for bonding.

Therefore, a total of 6 electrons are involved in the formation of the three covalent bonds in PCl3.

However, the statement is misleading because it focuses only on the bonding electrons. The total number of electrons involved in the PCl3 molecule is much higher, including the non-bonding electrons around the chlorine atoms.