Step-by-step explanation:
When it comes to assigning oxidation number to elements, the following rules should be observed;
1. Oxidation number of a neutral compound is zero and is equal to the sum of the oxidation numbers of the element.
2. Oxidation number of hydrogen is +1 except in hydrides where it is -1. Oxidation number of oxygen is -2 except in peroxides where it is -1.
3. For some elements, their oxidation number is equal to their group number.
(a) CaO
Let the oxidation number of Ca be x
Using rules 1 and 2;
Oxygen = -2
x + (-2) = 0
x - 2 = 0 ; x = 2
(d) KMnO4
K belongs to group 1 hence has oxidation number of +1
O = -2
Let the oxidation number of Mn be x
+ 1 + x + 4(-2) = 0
1 + x -8 = 0
x = +7
(b) NaHSO4
Na belongs to group 1 hence has oxidation number of +1
O = -2
Hydrogen = +1
Let the oxidation number of S be x
+ 1 + 1 + x + 4(-2) = 0
2 + x -8 = 0
x = +6
(e) NaH PO4
Na belongs to group 1 hence has oxidation number of +1
O = -2
Hydrogen = +1
Let the oxidation number of P be x
+ 1 + 1 + x + 4(-2) = 0
2 + x -8 = 0
x = +6
Fe304
Let the oxidation number of Fe be x
Using rules 1 and 2;
Oxygen = -2
3x + 4(-2) = 0
3x - 8 = 0 ; x = 8/3
For Fe3O4, two Fe atoms have an oxidation state of +3 and one of +2
(f) NaBH4
Na belongs to group 1 hence has oxidation number of +1
Hydrogen = +1
Let the oxidation number of B be x
+ 1 + x + 4(1) = 0
1 + x + 4 = 0
x = -5