Question

Which of the following is an incorrect formula?
A.$NaC{l_2}$
B.$BaS{O_4}$
C.${H_2}C{O_3}$
D.${P_2}{O_5}$

Answer 1

Hint: This question gives the knowledge about the molecular formula. The molecular formula is the representation of chemical compounds. It comprises the chemical symbols for the elements tailed by the numeric subscripts labelling the atoms of each element present in a molecule.

Complete step by step answer:
The molecular formula is the representation of chemical compounds. It comprises the chemical symbols for the elements tailed by the numeric subscripts labelling the atoms of each element present in a molecule. Valency is basically the combining capacity of molecules or atoms. Valency is also termed as combining power. Valency can be remembered as the total number of electrons present in the outermost shell.
Now to determine the incorrect molecular formula we will determine the valencies of the elements as follows:
A. Consider $NaC{l_2}$,
In this two elements are present, one is sodium and the other one is chlorine. The valency of sodium is one and the valency of chlorine is also one. So, on cross multiplying we get sodium chloride which is having a molecular formula as $NaCl$.
B. Consider $BaS{O_4}$,
In this two elements are present, one is barium and the other one is sulphate ion. The valency of barium is two and the valency of sulphate ion is also two. So, on cross multiplying we get barium sulphate which has a molecular formula as $BaS{O_4}$.
C. Consider ${H_2}C{O_3}$,
In this two elements are present, one is hydrogen and the other one is carbonate ion. The valency of hydrogen is one but here two hydrogens are present, so the valency becomes two and the valency of carbonate ions is two. So, on cross multiplying we get carbonic acid which has a molecular formula as ${H_2}C{O_3}$.
D. Consider ${P_2}{O_5}$,
In this two elements are present, one is phosphorus and the other one is oxide ion. The valency of phosphorus is five and the valency of oxide ion is two. So, on cross multiplying we get phosphorus pentoxide which has a molecular formula as ${P_2}{O_5}$.

Therefore, option A is the correct answer.

Note: Always remember that the valency is basically the combining capacity of molecules or atoms. Valency is also termed as combining power. Valency can be remembered as the total number of electrons present in the outermost shell.