Q.Angles of deviation for extreme colours are given for different prisms. Select the one having maximum dispersive power of its material. (A) 7°, 10° (B) 8°, 11° (C) 12°, 16° (D) 10°, 14°

[!TLDR] Dispersive power ratio (difference/sum, doubled) is largest for the pair 7 degrees and 10 degrees …

Dispersive power omega = (delta_V - delta_R)/delta_Y, with delta_Y approximated as the mean of the two given deviations, so omega = 2(difference)/(sum) for each pair. Computing this ratio for each option: (A) 7,10: 2x3/17 = 0.353; (B) 8,11: 2x3/19 = 0.316; (C) 12,16: 2x4/28 = 0.286; (D) 10,14: 2x4/24 = 0.33 …

Compute omega = 2(delta_V - delta_R)/(delta_V + delta_R) for each listed pair of deviation …

Comparing only the raw difference between the two deviations (which is largest for option C or D) rather than the properly normalised ratio to the m …