Which ions determine ionic conductivity of a salt solution?
Di water H2O has very poor conductivity. Because H+ and OH- only driven by the ionic product.

2 H2O &lt;=> H3O+ +OH-

If any other ions will be add the condictivity rises . So that can be for example by acids (H+), alcaline  solutions (OH-) and salts (Cations and anions). The conductivity of the salts  >>>>>> as of the water. So mainly in your case zinc and sulphate drive it. But to calculate correctly all 4 ions participate.