Special Graphs

8. A graph is connected if there exists a path between every pair of vertices.
   
   A connected component is a maximal connected subgraph.
   

   This graph is not connected because there is no path between vertices in the left pair and vertices in the right pair. The graph, however, contains two connected components: $\{1,2\}$ and $\{3,4\}$. Miriam Briskman, CC BY-NC 4.0.

   \documentclass[border=1pt]{standalone}
   \usepackage{tikz}
   
   \tikzset{
   vertex/.style={draw, circle, very thick, minimum size=1cm},
   edge/.style={very thick}
   }
   
   \begin{document}
   
   \begin{tikzpicture}
   
   % Component 1
   \node[vertex] (1) at (0,0) {$1$};
   \node[vertex] (2) at (2,0) {$2$};
   
   \draw[edge] (1) -- (2);
   
   % Component 2
   \node[vertex] (3) at (6,0) {$3$};
   \node[vertex] (4) at (8,0) {$4$};
   
   \draw[edge] (3) -- (4);
   
   \end{tikzpicture}
   
   \end{document}