Alkenes are also known as 

Alkenes are known as olefins which means oil-forming gas. 

They are called olefins because they form oily liquids on reaction with chlorine gas.

Why Alkenes are Called Olefins

1. Etymology: The term "olefin" originates from the Latin word oleum (oil) and the Greek word phaino (to appear). This is because alkenes form oily liquids when they react with halogens like chlorine or bromine.
2. Chemical Structure:
   Alkenes have the general formula CnH2n, indicating they are unsaturated hydrocarbons with a double bond. This unsaturation allows them to undergo addition reactions, such as halogenation, which results in the formation of oily products.
3. Distinctive Properties:
   • Alkenes are highly reactive due to the presence of the double bond.
   • This reactivity is the basis for their widespread use in industrial applications like polymer production (e.g., polyethylene).

Other Options

• Paraffins (b): This refers to alkanes, which are saturated hydrocarbons with single bonds and the formula CnH2n+2.
• Aliphatic Saturated Hydrocarbons (c): These are also alkanes, not alkenes.
• Arenes (d): Arenes are aromatic hydrocarbons, such as benzene, and do not include alkenes.