Question

Find the atomicity of the ${H_2}C{O_3}$ .
A. $3$
B. $4$
C. $5$
D. $6$

Answer 1

Hint: The total number of atoms that a compound has or the total number of atoms that constitute a compound is termed as atomicity. The carbonic acid is a polyatomic compound consisting of 2 atoms of hydrogen, one atom of carbon and three atoms of oxygen.

Complete step by step answer:
On the basis of atomicity, molecules are classified as:
Monoatomic- They are composed of only 1 atom e.g. \[He,{\text{ }}Ne,{\text{ }}Ar\] (all noble gases are monatomic)
Diatomic- They are composed of 2 atoms e.g. ${H_2},{N_2},{O_2}$ .
Triatomic- They are composed of 3 atoms e.g. \[{O_3}\] .
Polyatomic- They are composed of 3 or more atoms e.g. \[{P_4},\;{S_8}\] .
Thus, in the given compound ${H_2}C{O_3}$ , the atomicity is:
${H_2}C{O_3} = 2 \times 1 + 1 \times 1 + 3 \times 1 = 6$
Here, we can say that the number of atoms in the carbonic acid is equal to 6 and is a hexa atomic molecule and can also be included in the polyatomic species.

So, the correct answer is Option D .

Note:
All metals and some other elements in the periodic table, such as carbon, do not have a simple structure but consist of a very large and indefinite number of chains of atoms bonded together. Their atomicity cannot be determined easily and is usually considered as 1 because it is impossible to determine atomicity for an indefinite number of atoms. Atomicity may vary in different allotropes of the same element. This can be understood by the example of graphite and diamond which are allotropes of carbon.