what i think is it should be option d . take the example of a wheel graph. with w4 . it will contain 5 vertices. and its chromatic number will 3. so 5/3= 1.something . and the independent set . will be one. the option does not hold for it i think .
plus take a complete graph. and apply . independent set = zero. vertex = n . and chromatic number is n.
so c is saying 0>=1. not true.