Answer:
The 3p orbital of the element will be completely filled if it forms 3 bonds with other atoms.
Explanation:
Phosphorus is a element of 15 group and 3 period.
The electronic configuration of the phosphorous is:
1s²2s²2p⁶3s²3p³
The 3p orbital of phosphorous is singly filled by 3 electrons and if it shares more 3 electrons with other atom, its valence shell will be completely filled which makes it more stable. Hence, phosphorus makes 3 bonds like in PH₃ and PCl₃ .
