Final answer:
To form a tree on a graph with 10 nodes, you need at least 9 arcs.
Step-by-step explanation:
To form a tree on a graph with 10 nodes, you need at least 9 arcs. A tree is a connected graph with no cycles, which means that it has exactly one less edge than the number of nodes. In this case, since there are 10 nodes, the tree would have 9 arcs.