Question

The primary prefix is used in order to differentiate a cyclic compound from an acyclic compound.
A.Keto
B.Cyclo
C. Oxo
D. Halo

Answer 1

IUPAC names are basically combined of primary prefix, root word and primary suffix. By this each compound can be named unique. Primary prefixes are used to indicate the origin of the compound in IUPAC nomenclature. Prefixes are used to differentiate the cyclic and acyclic molecules in IUPAC nomenclature.

Complete step by step answer:
In IUPAC nomenclature, the root word is basically number of total carbons in a longest chain of that compound.

No. of carbons	Root word
1	Meth
2	Eth
3	Prop
4	But
5	Pent

… and so on.
The primary suffix is basically used to differentiate between the saturated compounds (Alkanes) and unsaturated compounds (Alkene and Alkynes).

compound	suffix
Alkane	ane
Alkene	Ene
Alkyne	Yne

If there are more than one suffix. Then one of those suffixes is considered a secondary suffix.
Example: Methanol (Alkanol) , here ‘ol’ is a secondary suffix.
The primary prefixes are basically used to differentiate between cyclic compound and noncyclic or chain compound. For cyclic compound prefix s ‘cyclo’. if there are any side chains or groups are present then secondary prefixes like ‘methyl’, ‘ethyl’ are used.
So, the primary prefix ’cyclo’ is used in order to differentiate a cyclic compound from an acyclic compound.

Hence option C is correct.

Note:
For example, the structure of lindane is,

The IUPAC name of lindane is gamma-hexachlorocyclohexane. It is also called benzene hexachloride.
In this structure two chlorine atom which are cis to each other are at gamma position, that is why gamma is written in the IUPAC name.
It is a cyclic compound so “cyclo” prefix is used. Six carbon is present in the ring so “hex” is the word root. And “ane” is used as the primary suffix.
There are six chlorine atoms are present that is why “hexa cholo” is added in the name.