The minimum number of colours required to colour the vertices of a cycle with $n$ nodes in such a way that no two adjacent nodes have the same colour is
Thanx @Pragy Agarwal
Chromatic number will be $3$ for when $n$ is odd and will be $2$ when $n$ is even. Option (D) is a representation for this, hence the correct answer
@Gupta731 just substitute n = 3 and n = 4 in given equation. You will get the desired answer.