The result is easy to verify for n=2,3,4…7. Now we consider for n ≥ 8. Here the vertices
v
2
′, v
3
′,….v
′ are incident with atmost four edges. So there is a possibility of assigning five
colours to every M(P
n-1
n
) to produce a b-chromatic colouring. Suppose if we assign more than five
colours, it contradicts the definition of b-colouring. Thus by the colouring procedure the above
said colouring is maximum and b-chromatic.