Let G be the non-planar graph with the minimum possible number of edge...
Explanation: According to Kuratowski’s Theorem, a graph is planar if and only if it does not contain any subdivisions of the graphs K5 or K3,3.
That means K5 and K3,3 are minimum non-planar graphs. These graphs have 5 vertices with 10 edges in K5 and 6 vertices with 9 edges in K3,3 graph.
So, graph K5 has minimum vertices and maximum edges than K3,3.
So, option (B) is correct.
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Let G be the non-planar graph with the minimum possible number of edge...
Explanation:
To understand why the correct answer is option 'B', we need to first understand the concept of planar graphs and non-planar graphs.
Planar Graph:
A graph is said to be planar if it can be drawn on a plane without any edges crossing each other.
Non-Planar Graph:
A graph is said to be non-planar if it cannot be drawn on a plane without any edges crossing each other.
Now, let's analyze each option one by one.
Option (a):
If G had 5 vertices and 9 edges, we can draw a planar graph with these specifications. For example, we can draw a complete graph K5 which has 5 vertices and 10 edges. If we remove one edge from K5, we get a planar graph with 5 vertices and 9 edges.
Option (c):
If G had 5 vertices and 10 edges, we can draw a planar graph with these specifications. For example, we can draw a bipartite graph K3,3 which has 6 vertices and 9 edges. If we remove one edge from K3,3, we get a planar graph with 5 vertices and 8 edges. So, this option is also not correct.
Option (d):
If G had 6 vertices and 10 edges, we can draw a planar graph with these specifications. For example, we can draw a complete graph K6 which has 6 vertices and 15 edges. If we remove 5 edges from K6, we get a planar graph with 6 vertices and 10 edges.
Option (b):
If G had 6 vertices and 9 edges, we cannot draw a planar graph with these specifications. This is because of the following theorem:
Euler's Formula for Planar Graphs:
For any connected planar graph, we have V - E + F = 2, where V is the number of vertices, E is the number of edges and F is the number of faces.
If we assume that G has 6 vertices and 9 edges, then we can use Euler's formula to find the number of faces. We have:
6 - 9 + F = 2
F = 5
So, there are 5 faces in G. However, this is not possible because the minimum number of faces in any non-planar graph is 6. Therefore, G cannot have 6 vertices and 9 edges, and the correct answer is option (b).
Conclusion:
The minimum possible number of edges in a non-planar graph with 6 vertices is 9. Therefore, option (b) is the correct answer.