Now, it is isomorphic to its complement so no. Of edges in its complement graph will also be n.

No. Of edges in graph G + No. Of edges in graph G'= no. Of edges in complete graph ( $\frac{n(n-1)}2$ ).

n+n= $\frac{n(n-1)}2$

2n= $\frac{n(n-1)}2 $

4n = n(n-1)

4n=n^2-n

$n^{2}$-5n=0

n(n-5)=0

n=5.