The primary rainbow is formed by total internal reflection in the raindrop once. It is between 41° to 42°. The secondary rainbow is formed by total internal reflection in the raindrop twice. It is between 51° to 54°. Thus, option (d) is correct. Now, destructive interference is the reason that the band is dark. Hence, (a) is correct. Scattering of light by minute particles happens all over the sky and doesn’t affect the formation of the rainbow or Alexandra’s band. Hence, (b) is incorrect. Moreover, there is no “extra” absorption of light in this region. Hence, (c) is incorrect. This band is not a physical region, but a region formed in our eyes like the rainbows.
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