Question

The total number of atoms present in $CO_3^{2 - }$ is _______.
A: $5$
B: $3$
C: $4$
D: $2$

Answer 1

Hint: A molecule is defined as a substance which is made up of atoms. Anything which we see around is composed of atoms. Atoms are the smallest unit of ordinary matter that forms a chemical element. Atoms are very small. The size of an atom is measured in picometers.

Complete step by step answer:
We know atoms are the smallest unit of anything which we see around us. A molecule is composed of two or more atoms. Oxygen is an element that is made up of atoms of oxygen. Similarly, hydrogen is also an element composed of hydrogen atoms. When two atoms of hydrogen combine with one atom of oxygen one water molecule is formed. The chemical formula of water is ${H_2}O$. The number of atoms in any molecule is calculated by adding subscripts of each element. If there is no subscript then it is taken one. Like in water, the subscript of hydrogen is $2$ and oxygen is $1$ (as it is not written). So, the total number of atoms is $2 + 1 = 3$ . Similarly, we can calculate the number of atoms in a given molecule that is $C{O_3}$. The subscript of carbon is $1$ and oxygen is $3$. So, the total number of atoms can be written as:
Total number of atoms$ = 3 + 1 = 4$ .

So, the correct answer is option C that is $4$.

Note:
Isotopes are the atoms of the same element which have different mass numbers but the same atomic number. Similarly, isobars are atoms of different elements which have the same mass number but a different atomic number.