Question

Which of the following compounds are not known?
A. $P{{H}_{3}}$
B. $P{{I}_{3}}$
C. $NC{{l}_{5}}$
D. All of these

Answer 1

A chemical compound can be defined as a chemical substance which consists of many identical molecules or molecules entities i.e. composed of atoms from more than one element held together by chemical bonds.

Complete step by step answer:
A molecule which consists of atoms of only one element is therefore not a compound and there are four types of compounds depending on the bonding between their constituent atoms that bind them together, covalent compounds in which molecules held together by covalent bonds, ionic compounds held together by ionic bonds, intermetallic compounds held together by metallic bonds and some coordinate compounds which held together by coordinate covalent bond.
Any metal or non-metal can form chemical compounds according to their valency and valency is the term which defines the outermost electrons which are free to form bonds. In the given options the valency of phosphorus is 5 therefore it can form $P{{H}_{3}}$ and $P{{I}_{3}}$ while nitrogen shows the valency 4 so we can say that it does not have d orbitals which expand its covalence beyond four so it can-not form $NC{{l}_{5}}$ compound.
Thus we can say that option C is the correct answer. Nitrogen will not form more than 4 atoms because valency shown by nitrogen is 4.

Note: Valency can be defined as the combining capacity of an atom and in also be defined as the number of bonds that an atom can form as part of a compound is expressed as the valency of that element and valence electrons are the electrons that are present in the outermost orbital of the atom.