Question

Which of the following represents a correct chemical formula?
 $ (A)CaCl $
 $ (B)BiP{O_4} $
 $ (C)NaS{O_4} $
 $ (D)NaS $

Answer 1

Hint: A chemical formula is a representation of a chemical compound (organic or inorganic) in the form of chemical symbols of the elements present in that compound. In order to identify the correct chemical formula of a substance, we need to understand the concept of valency because ions form compounds to fulfil their valency and attain a stable noble gas configuration.

Complete Step By Step Answer:
We know that a chemical formula is a representation of a chemical compound (organic or inorganic) in the form of chemical symbols of the elements present in that compound.
Valency of an element is equal to the number of electrons that it can lose or gain in order to attain noble gas configuration and form a stable compound.
Valency of Ca is $ 2 $ because it forms $ C{a^{2 + }} $ ion and Cl is $ 1 $ because it forms $ C{l^ - } $ ion . So, the correct formula for calcium chloride is found to be $ CaC{l_2} $ ​.
Valency of Bi is $ 3 $ because it forms $ B{i^{3 + }} $ ion and that of phosphate ion is also $ 3 $ . Hence, the correct formula of bismuth phosphate is $ BiP{O_4} $ ​.
Similarly, valency of Na is $ 1 $ and sulphate​ is $ 2 $ . Hence, the correct formula of sodium sulphate is $ N{a_2}S{O_4} $ .
Valency of Na is $ 1 $ and that of sulphur is $ 2 $ . Hence, the correct formula of sodium sulphide is $ N{a_2}S $ .
Therefore, the correct option is $ (B)BiP{O_4}. $

Note:
We should remember that while writing the chemical formula of a chemical compound, the valency of each element or ion in the compound should be satisfied because the ions combine with each other to form a stable chemical compound. This happens because the elements on gaining or losing electrons attain noble gas configuration.