|Definition: A graph $G = (V(G), E(G))$ is a Null Graph if there are no edges in the graph, that is $\mid \: E(G) \: \mid = 0$.|
Null graphs are denoted as $N_n$ where n denotes the number of vertices of the graph. Below are some examples of null graphs, namely $N_2$, $N_3$, and $N_4$
We should note that null graphs always have degree $0$ since there are no edges joining the vertices. Null graphs also have $0$ edges clearly. We can say that null graphs are also 0-regular.
Furthermore the only null graph graph that is connected is $N_1$. All other null graphs are disconnected.