What is the oxidation number of the chromium atom in li 2 cro4?

You can find the oxidation number of a certain element in a compound if you add up their oxidation numbers to the net charge. This is just a simple algebraic equation. Let x be the oxidation number of Cr. Since the compound is neutral, the net charge is 0. Thus,

oxidation number for Li: + 1

Oxidation number of O: - 2

0 = 2 (+1) + x + 4 (-2)

Solving for x,

x = + 6

Thus, the oxidation number of Cr is + 6.