Q72,paper 3,J 12. G1 and G2 are two graphs as shown.

(A) Both G1 and G2 are planar graphs.
(B) Both G1 and G2 are not planar graphs.
(C) G1 is planar and G2 is not planar graph.
(D) G1 is not planar and G2 is planar graph.
Answer (d).
Explanation.
Let G be a connected planar graph, and let v, e and f denote, respectively, the numbers of vertices, edges, and faces in a plane drawing of G.
Then property 1, v - e + f = 2.
Property 2. e ≤ 3v - 6.
Property 3. e<=2v-4.

In graph G1, there are 6 vertices and six edges.then then property 2 . (6<= 18-6)) and in G1 property 3 is also satisfied.
in graph G2.there are 6 vertices and 12 edges then property3. fails.