Rules to Remember
* Oxygen: Oxygen usually has an oxidation state of -2, except in peroxides (like H₂O₂) where it's -1.
* Sodium: Sodium is in group 1 of the periodic table, so it always has an oxidation state of +1.
* The sum of oxidation states in a neutral compound is zero.
Calculation
1. Oxygen: We have 7 oxygen atoms, each with an oxidation state of -2, giving a total of -14.
2. Sodium: We have 2 sodium atoms, each with an oxidation state of +1, giving a total of +2.
3. Chromium: Let the oxidation state of chromium be 'x'. Since we have two chromium atoms, the total contribution from chromium is 2x.
Equation:
+2 + 2x - 14 = 0
Solving for x:
2x = 12
x = +6
Therefore:
* Sodium (Na): +1
* Chromium (Cr): +6
* Oxygen (O): -2
