Reason (R): Dispersive power of prism is non zero while that of glass slab is zero.
Solution:
A prism disperses light because its non-parallel surfaces separate colors due to varying refractive indices. A rectangular slab also disperses light internally, but the emergent rays are parallel, resulting in no net angular dispersion. Dispersive power is a material property and is non-zero for any dispersive medium, including glass slabs.
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