Number of C – atoms in the longest chain is 3
Parent alkane is Propane
Root word Prop
Suffix – ol
The carbon atom to which –OH group is attached is numbered as C1 followed by other carbon atoms numbering.
∴ IUPAC name of CH3CH2CH2OH is Propan-1-ol
Number of C – atoms in the longest chain – 1
Parent alkane – Methane
Root word – meth
Suffix functional group is acid – oic acid
'oic acid' replaces 'e' of methane
∴ IUPAC name of HCOOH is Methanoic acid.
(c) CH3 – CH = CH - CH3
Number of C – atoms in the longest chain – 4
Parent alkane – Butane
Root word – but
Suffix – ene (in case of alkene)
∴ its a butene
The numbering of C atom starts from the carbon atom to double bond. The position of the double bond is between the second and third C atom of which '2' is the least.
∴ IUPAC name of CH3 – CH = CH - CH3 is But – 2 – ene.