2 votes 2 votes Let G be a planar Graph Such that every phase is bordered by exactly 3 edges which of the following can never be value for X(G) a)2 b)3 C)4 d)none of these Graph Theory graph-theory discrete-mathematics graph-connectivity graph-coloring + – Parshu gate asked Nov 11, 2017 • retagged Oct 9, 2023 by Hira Thakur Parshu gate 1.2k views answer comment Share Follow See all 3 Comments See all 3 3 Comments reply joshi_nitish commented Nov 11, 2017 reply Follow Share Let G be a planar Graph Such that every phase is bordered by exactly 3 edges since graph conain odd length cycle, its chromatic no. X(G)>=3 so 2 can never be X(G), hence option a is correct. 6 votes 6 votes Ashwani Kumar 2 commented Nov 11, 2017 reply Follow Share Yes option a) is correct 2 is not possible because when a region consist exactly 3 edges means vertices joining them are adjacent and should be colored uniquely. You can also observe this with example below 4 votes 4 votes Lakshman Bhaiya commented Feb 3, 2020 reply Follow Share $\chi (G) \leq \Delta (G) + 1$ 0 votes 0 votes Please log in or register to add a comment.