Is $ BC{{l}_{3}} $ an electron deficient compound.

Hint : We know that compounds having less number of electrons than the required amount to attain maximum stability is known as electron deficient species. Generally these compounds don’t have enough electrons to form normal covalent bonds. For making their stability generally atoms have to need eight electrons in their outermost shell.

Complete Step By Step Answer:
On the basis of the number of electrons present in central atoms the compounds can be divided into three categories that are electron deficient, electron precise and electron rich compounds. Electron deficient compounds: In this type of compounds the central atoms do not have sufficient number of valence electrons to form covalent bonds.
Electron precise compounds: In this type of compounds the central atoms have sufficient number of valence electrons to form covalent bonds. Electron rich compounds: In this type of compounds the central atoms have sufficient number of valence electrons to form covalent bonds. Electron rich compounds: In this type of compounds the central atoms have an excess number of valence electrons to form covalent bonds.
Yes $ BC{{l}_{3}} $ is an electron-deficient compound. As boron has three valence electrons, it forms three single bonds with chlorine, In total the boron atom gives six electrons in the outermost shell. It still lacks two electrons to complete its octet. So $ BC{{l}_{3}} $ is an electron-deficient compound.

Note :
Remember that it is to be noted that in an electron deficient compound, the octet of the electron is not complete, that is the central atom has an incomplete octet. Therefore, it requires electrons to complete their octet.