So I'm asked to find the chromatic number for the given graph by colouring the vertices using the minimum number of required colours. My attempt at doing so is below but I was wondering if someone could confirm whether I coloured it correctly? Are there any vertices that should be a different colour/should there be more or less colours used? Did I misplace any colours?
I was also wondering if there is some rule or formula to figure out the chromatic number for a graph?
I'd appreciate some help or confirmation.
Link to graph: https://imgur.com/a/1UVydLo
Nodes $8, 14, 15$ form a triangle. Therefore it is not possible to color the graph with less than $3$ colors. Since you used $3$ colors and no two adjacent nodes have the same color, your coloring is correct.