Question

A formula unit indicates:
A.the highest reduced ratio of ions in the compound
B.the lowest reduced ratio of uncharged molecules in the compound
C.the lowest reduced ratio of ions in the compound
D.both A and B

Answer 1

A formula unit is the representation of the empirical formula for an ionic compound It is given as the lowest ratio possible of the cations and anions in a given ionic compound.

Complete step by step answer:
We know that table salt has the chemical formula unit of ${\text{NaCl}}$, by which we mean that the elements sodium and chloride ions are in a ratio of 1:1. Ammonium nitrite has the chemical formula of ${\text{N}}{{\text{H}}_{\text{4}}}{\text{N}}{{\text{O}}_{\text{2}}}$, in which the ions are present in a ratio of 1:1.
We don’t write the formula unit is as ${\text{N}}{{\text{H}}_{\text{2}}}{\text{O}}$nor as ${{\text{N}}_{\text{2}}}{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}$, because in the formula we show the ions that composes the ionic compound. Another example is of aluminium sulphate, which have a formula unit of ${\text{A}}{{\text{l}}_{\text{2}}}{\left( {{\text{S}}{{\text{O}}_{\text{4}}}} \right)_{\text{3}}}$. This formula indicates that the aluminum and sulphate ions are present in a ratio of 2:3. Also parentheses around the ${\text{S}}{{\text{O}}_{\text{4}}}$, which indicates that here we have 3 sulphate ions.

We know that the formula unit represents the ratio of the compound. A formula unit is represented as the lowest reduced ratio of molecules present in the compound.
Therefore, we can say that C is the correct answer. A, B and D are incorrect option

So, Option C is correct.

Note: Students may get confused between formula unit and molecular formula. By formula unit we represent the ratio of the ions which is present in a compound. The molecular formula of a compound represents the atoms and the number of atoms present in the compound. The number of the atoms in the compound are written in the form of suffix.