See the given 2 graphs are vertex disjoint since the labels used in the 2 graphs for vertices are different .Not a single vertex appears in both graph G1 and G2 , since for G1 ∩ G2 , we require :
V1 ∩ V2 for common vertices
and E1 ∩ E2 for common edges but before that the vertices which are incident on that particular edge should also be common i both the graphs.
So according to the above graph , they are vertex disjoint and for vertex disjoint situation , even graphs do not exist at all but for edge disjoint situation , graph may exist.
So the above is a vertex disjoint one.
Hence no of edges = no of vertices in G1 ∩ G2 = 0
Hence no of edges in G = 0