What is the maximum number of edges in an acyclic undirected graph with $$n$$ vertices?

Let $$G$$ be an arbitrary graph with $$n$$ nodes and $$k$$ components. If a vertex is removed from $$G$$, the number of components in the resultant graph must necessarily lie between

Maximum number of edges in a n - node undirected graph without self loops is

The number of distinct simple graph with upto three nodes is