Question

Identify the compound in which the total number of constituent atoms present in a molecule is even:
A. Ferric oxide
B. Calcium hydrogen sulfide
C. Calcium nitrate
D. Sodium nitrate

Answer 1

Hint: To answer this question write the chemical formula of each molecule given in the options and then count the number of atoms present in the formula. The molecule which has an even number of atoms is your answer.

Complete step by step answer:

Let’s solve this answer by explaining each option -

Option A, the chemical formula of ferric oxide can be written as $Fe_{ 2 }O_{ 3 }$. This formula has two iron atoms and three oxygen atoms. So, the total number of atoms is 5 and it is an odd number.

Option B, the chemical formula of calcium hydrogen sulfide can be written as $CaH_{ 2 }S$. This formula has one calcium atom, two hydrogen atoms, and one sulfur atom. So, the total number of atoms is 4 and it is an even number.

Option C, the chemical formula of calcium nitrate can be written as $Ca(NO_{ 3 })_{ 2 }$. This formula has one calcium atom, two nitrogen atoms, and six oxygen atoms. So, the total number of atoms is 9 and it is an odd number.

Option D, the chemical formula of sodium nitrate can be written as $NaNO_{ 3 }$. This formula has one sodium atom, one nitrogen atom, and three oxygen atoms. So, the total number of atoms is 5 and it is an odd number.

Therefore, we can conclude that the correct answer to this question is option B.

Note: You should not misunderstand the formulae of oxides of iron -
One of the oxides is FeO, which is known as ferrous oxide due to (+2) oxidation state of iron. Another one is $Fe_{ 2 }O_{ 3 }$ which is known as ferric oxide due to (+3) oxidation state of iron in this compound.