Question

How do we know which chemical comes after mixing 3 or more chemical, on paper work like balance equation, example : H2 + NaCl + So4 ~ ? What is the product how we can know

Answer 1

Chemical equations follow experiment. Experiment does not follow chemical equations.

Explanation:

So how do you know? You do the experiment, and interpret the result. You know that there is a mass balance. If there are 10 g of reactant, there can be at most 10 g of product. In practice, you are not even going to get 10 g. There is also a balance in electronic charge; there does not seem to be one on your equation.

So to your question; you mixed dihydrogen gas, sodium chloride, and sulfate dianion (i.e. `SO_4^(2-)`). This does not correspond to any chemical reaction I know. I think you have made a mistake transcribing the question.