$1-$ The matching number

$u(G)$ is the maximum size of a matching in $G.$

$u(K_n)=?$

$2-$ Apply Dijkstra's algorithm to find the shortest path.

$3-$ Apply Kruskal's algorithm to find a minimum spanning tree

$4-$ Find the chromatic number of the Petersen graph, star graph, complete graph, complete

bipartite graph, etc.

$5-$ Express the Euler's formula for planar graphs.