What is a homologous series? Give an example.

(N/A) homologous series is a group or a series of organic compounds that have the same functional group and similar chemical properties,and in which the successive members differ by a $-CH_{2}-$ unit.
$(I)$ The members of a homologous series can be represented by a general molecular formula.
$(II)$ The successive members differ from each other in molecular formula by a $-CH_{2}-$ unit.
$(III)$ All compounds of a homologous series contain the same functional group.
$(IV)$ The compounds of a homologous series are prepared by general methods and exhibit similar chemical properties.
$(V)$ The physical properties of members of a homologous series change gradually with an increase in molecular mass.

Homologous series / General formula	Examples
Alkane series: $C_{n}H_{2n+2}$	$C_{2}H_{6}, C_{3}H_{8}, C_{4}H_{10}$
Alkene series: $C_{n}H_{2n}$	$C_{2}H_{4}, C_{3}H_{6}, C_{4}H_{8}$
Alkyne series: $C_{n}H_{2n-2}$	$C_{2}H_{2}, C_{3}H_{4}, C_{4}H_{6}$
Alcohol series: $C_{n}H_{2n+1}OH$	$CH_{3}OH, C_{2}H_{5}OH, C_{3}H_{7}OH$
Acid series: $C_{n}H_{2n+1}COOH$	$CH_{3}COOH, C_{2}H_{5}COOH$