During purification of many cytosolic proteins, it is important to
include either dithiothreitol or b-mercaptoethanol in the
buffers. why?

To reduce thiol-groups of the protein

Explanation:

Dithiothreitol of b-mercaptoethanol act as reducing agents. Including them in a buffer would prevent oxidation of thiol-groups in amino acids of the protein and preventing its denaturation.

one part of the electromagnetic spectrum that arrives on earth as solar radiation from the sun is the visible spectrum. wavelengths of the visible spectrum combine to form what we refer to as

answer - d) ultraviolet radiation.

violet /   380–450 nm / 668–789 thz

violet is number 1 in the chart of visible light.