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Graph Theory

GATE CSE 2022 · Q50

MSQ2 marksMedium

Time

The following simple undirected graph is referred to as the Peterson graph. Which of the following statements is/are TRUE?

GATE CSE 2022 Q50 diagram

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Solution

Step-by-step verified solution

Official answer: A) The chromatic number of the graph is 3.; B) The graph has a Hamiltonian path.; C) The following graph is isomorphic to the Peterson graph.

Graph Theory

Let us analyze each statement for the Petersen graph G=(V,E)G = (V, E) with ∣V∣=10|V| = 10 and ∣E∣=15|E| = 15:

  • (A) True: The Petersen graph contains odd cycles (it has 5-cycles, and its girth is 5), so it is not bipartite and requires at least 3 colors. It can be 3-colored (for instance, color the outer 5-cycle with colors 1,2,1,2,31, 2, 1, 2, 3 and color the corresponding adjacent inner vertices properly with 3,3,2,1,13, 3, 2, 1, 1). Hence, its chromatic number is χ(G)=3\chi(G) = 3.

  • (B) True: The Petersen graph is famous for being non-Hamiltonian (it does not contain a Hamiltonian cycle), but it does possess a Hamiltonian path (a simple path visiting all 10 vertices).

  • (C) True: The graph shown is a known 3-regular graph with 10 vertices, girth 5, and diameter 2. It is isomorphic to the Petersen graph.

  • (D) False: The independence number (size of the maximum independent set) of the Petersen graph is α(G)=4\alpha(G) = 4, not 3 (e.g., choosing two independent vertices from the outer 5-cycle and two independent vertices from the inner star).

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This Graph Theory previous year question is Q50 of the GATE CSE 2022 paper. Find more GATE CSE PYQs on Graph Theory in Engineering Mathematics, or browse all GATE CSE PYQs.

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GateAI solution cardGATE CSE 2022 · Q50 · MSQ

The following simple undirected graph is referred to as the Peterson graph. Which of the following statements is/are TRUE?

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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.