Question

Heterocyclic compounds are _____________ in nature.
A. aliphatic
B. aromatic
C. aliphatic or aromatic
D. inorganic

Answer 1

Hint: Generally, cyclic compounds which are said to be aromatic, contain rings which have carbons present in them. However, this is not true. And open chains need not necessarily be made up of only carbon atoms.

Complete answer:
The compounds which are cyclic whose rings don't only contain carbon atoms could also be aromatic, as well. In heterocyclic compounds one or quite one atom of carbon present within the ring is displaced by atoms of other elements. These are then called heteroatoms. Heteroatoms in organic compounds generally nitrogen, oxygen, or sulphur atoms. In aromatic heterocyclic compounds, it's not only the carbon atoms' orbital that participate within the forming the aromatic system.
Moreover, orbitals of the heteroatoms participate within the $\pi $ system here too. Pyridine, as an example, is such an aromatic heterocycle. Each of the six ring atoms is $s{{p}^{2}}$-hybridized, while the molecule possesses six $\pi $ electrons. The lone electron pair of pyridine's nitrogen atom occupies a $s{{p}^{2}}$ orbital. These electrons are therefore not $\pi $ electrons. The remaining two $s{{p}^{2}}$ orbital of the nitrogen overlap with $s{{p}^{2}}$ orbital of the adjacent carbons, forming two $\sigma $ bonds. The $\pi $ system is the result of the overlapping of the nitrogen's and carbons' $\pi $ orbitals, which are perpendicular to the ring plane.
So it aliphatics and aromaticity does not depend upon the atom that is present in the chain or ring. Even atoms apart from carbon(heterocyclic) can also be aliphatic or aromatic.

So, we get our answer option C.

Note:
Heterocyclic compounds find their use in a wide range of applications. They are generally used as pharmaceuticals, as chemicals for agriculture and also as veterinary products. They also find applications as sanitizers, developers, antioxidants, as corrosion inhibitors and in the dyeing industry.