The focal length of a thin convex lens for red and blue rays are...

Dispersive power is ratio of angular dispersion and mean deviation.

It can be written in terms of focal length as,

$\omega = \dfrac{{f}_{r} - {f}_{b}}{fy}$

Here ${f}_{r} = 100cm$

${f}_{b} = 96. 8cm$

${f}_{y} = \sqrt{{f}_{b} \times {f}_{r}}$

$= \sqrt{96. 8 \times 100}$

$\approx 98. 34cm$

$∴$ Dispersive power

$\omega = \dfrac{{f}_{r} - {f}_{b}}{fy}$

$= \dfrac{100 - 96. 8}{98. 34}$

$\approx 0. 0325$
Hence, the dispersive power of the material of the lens is $0. 0325$.