Which of the following is an essential fatty acid?
Linoleic acid
Alpha linolenic acid
Both of the above
None of the above
The fatty acids that are required by humans, but are not synthesized in the body, hence need to be supplied in the diet are known as essential fatty acid (EFA). Humans lack the enzymes that can introduce double bond beyond 9th Carbon.
They are Polyunsaturated Fatty Acid namely:

Linoleic acid.
Alpha linolenic acid.
Arachidonic acid is considered as semi-essential fatty acid as, it can be synthesized from linoleic acid.