Focal lengths of the convex lens:For red rays, fr​ =100 cmFor yellow rays, fy​ =98 cmFor violet rays, fv​ =96 cmLetμr​ = Refractive index for the red colourμy​ = Refractive index for the yellow colourμv​ = Refractive index for the violet colourFocal length of a lens (f) is given byf1​=(μ−1)(R1​1​−R2​1​)Here, μ is the refractive index and R1​ and R2​ are the radii of curvatures of the lens.Thus, we have(μ−1)=f1​×(R1​1​−R2​1​)1​⇒ (μ−1)=fk​...........[k=(R1​1​−R2​1​)1​]For red rays, μr​ −1=100k​For yellow rays, μy​ −1=98k​,For violet rays, μv​ −1=96k​Dispersive power (ω) is given by ω=μy​−1μv​−μr​​Substituting the values, we getω=(μy​−1)(μv​−1)−(μr​−1)​⇒ω=0.0408Thus, the dispersive power of the material of the lens is 0.0408.