Zinc metal; copper (ii) sulfate solution
(a) molecular equation:
(b) total ionic equation:
(c) net ionic equation:

A =Zn(s) + CuSO₄ (aq)    →    ZnSO₄ (aq)  + Cu (s)

B = Zn(s) + Cu²⁺(aq) + SO₄²⁻ (aq)    →    Zn²⁺(aq) + SO₄²⁻(aq)  + Cu(s)

C = Zn(s) + Cu²⁺(aq)    →    Zn²⁺  (aq) + Cu(s)

Explanation:

The reactivity of zinc is higher than than copper. That's why when zinc is added into the copper(ii) sulfate it displace the copper and form zinc sulfate solution.

Molecular equation:

Zn(s) + CuSO₄ (aq)    →    ZnSO₄ (aq) + Cu(s)

It is redox reaction. The copper is reduced because its oxidation number reduced from +2 to zero and zinc is oxidize its oxidation state increase from zero to +2.

Ionic equation:

Zn(s) + Cu²⁺(aq) + SO₄²⁻ (aq)    →    Zn²⁺(aq) + SO₄²⁻(aq)  + Cu(s)

Net ionic equation:

Zn(s) + Cu²⁺(aq)    →    Zn²⁺  (aq) + Cu(s)

The  SO₄²⁻ are spectator ions that's why these are not written in net ionic equation.

Spectator ions:

These ions are same in both side of chemical reaction. These ions are cancel out. Their presence can not effect the equilibrium of reaction that's why these ions are omitted in net ionic equation.  

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !

a corroding iron, if that's one of your choices