Question

Why are three c=c double bonds in benzene ring said to be inert and more stable than c=c double bond in alkene ?

Answer 1

Alkanes, Alkenes and alkynes fall into the category of aliphatic. The benzene ring falls into the category of aromatic hydrocarbons and are very stable. To be an aromatic system the compound has to have the following requirements:
The molecule is cyclic (a ring of atoms)
The molecule is planar (all atoms in the molecule lie in the same plane)
The molecule is fully conjugated (p orbitals at every atom in the ring)
The molecule has 4n+2 π electrons (n=0 or any positive integer)
The compounds that fall into the aromatic are defined as significantly more stable than would be predicted on the basis of the most stable Lewis structural formula written for it.

Answer 2

Agreed Tara