Question 1
The oxidation numbers of calcium and chromium in the compound 
Explanation: Calcium is in the second group of the periodic table, so its oxidation number will always be 
. This is true for all alkaline earth metals.
As for chromium, the dichromate anion (
) has an overall charge of 
. Each oxygen atom will always have an oxidation number of 
as well, so the oxygens would have a total negative charge of 
. The sum of the oxidation numbers have to equal the overall charge, so chromium must be used to balance the negative charges from the oxygen. To bring the overall charge to 
, the two chromiums have to have total charge of 
, giving each an oxidation number of 
.
. This is true for all alkaline earth metals.
As for chromium, the dichromate anion () has an overall charge of . Each oxygen atom will always have an oxidation number of as well, so the oxygens would have a total negative charge of . The sum of the oxidation numbers have to equal the overall charge, so chromium must be used to balance the negative charges from the oxygen. To bring the overall charge to , the two chromiums have to have total charge of , giving each an oxidation number of .