In this case, since we know the balanced chemical reaction, we are first able to realize there is a 1:3 mole ratio between zinc phosphate and zinc chloride; it means that we can first compute the moles of the desired product via stoichiometry:
Next, since those moles are associated with the theoretical yield of zinc chloride, we obtain the corresponding mass:
Finally, we compute the percent yield by diving the actual yield (18 g) by the theoretical yield:
I looked on a solubility chart to answer this question, and hydroxides are generally insoluble (with some exceptions of course). However, it says to consider as an insoluble substance, though it may be moderately soluble.
The answer that you are most likely looking for is: Yes, a precipitate does form - this is due to the double placement reaction:
An element, by definition, always has the same number of protons. Sodium, element 11, has 11 protons. Anything with 11 protons is a sodium atom, regardless of the number of neutrons, electrons, or politicians.