[RossMoesis]

Hello, I'm a chemistry undergrad at the university of oklahoma and in the process of taking advanced inorganic chemistry but I'm struggling with this problem. I need to identify the oxides correspnding to the following bases: 

A- potassium hydroxide
B- Chromium (III) hydroxide, Cr(OH)₃     

Plus is there an easy way to identify the changes in oxidation states in these equations?

A-  Mg(s) + FeSO₄(aq) --> Fe(s) + MgSO₄

B- 2 HNO₃(aq) + 3 H₂S(aq)  ---> 2 NO(g) + 3 S(s) + 4 H₂O(l)


Any help would be greatly appreciated, I have a text next week 

[Yggdrasil]

Plus is there an easy way to identify the changes in oxidation states in these equations?

A-  Mg(s) + FeSO₄(aq) --> Fe(s) + MgSO₄

B- 2 HNO₃(aq) + 3 H₂S(aq)  ---> 2 NO(g) + 3 S(s) + 4 H₂O(l)

For A, you have to remember two easy rules to determine the oxidation state of metals:
1) the oxidation state of the pure metal is 0
2) the oxidation state of a metal ion is equal to its charge

For B, you can figure out the oxidation states of the N and S by using another set of simple rules (these rules are applicable to redox reactions involving non-metals, the other set of rules are for redox reactions with metals):
1) the oxidation state of oxygen is almost always -2 (exceptions: peroxides and superoxides)
2) the oxidation state of hydrogen is almost always +1 (except when in an ionic compound with a metal)
3) the sum of the oxidation states of the atoms in a molecule is equal to its charge

For example, in HNO₃, an uncharged molecule, you know that:

ON_H + ON_N + 3ON_O = 0

where ON_H = the oxidation state of H in HNO₃
ON_N = the oxidation state of N in HNO₃, etc.

By rules (1) and (2), we know that ON_H = +1 and ON_O = -2.  Therefore:

1 + ON_N + 3 x (-2) = 0

By simple algebra, you can find ON_N = +5

Repeat this process for the other compounds in the reaction to find how the oxidation states change for all atoms involved.