Final answer:
Option C) PbSO4 and Pb3(PO4)2 is the pair of compounds that is insoluble in water based on solubility guidelines, as lead(II) sulfate and lead(II) phosphate do not dissolve in water.
Step-by-step explanation:
The question asks which pair of compounds is insoluble in water. Using solubility guidelines, we know that nitrates and compounds of group 1 elements, like Na and NH4, are generally soluble. Moreover, compounds containing sulfate (SO42-) are usually soluble, except for those coupled with Pb2+, Ba2+, and a few others. Given the pairs in the options, PbSO4 (lead(II) sulfate) and Pb3(PO4)2 (lead(II) phosphate) are both insoluble in water since lead(II) compounds are an exception to the general rule of soluble sulfates and phosphates are insoluble in general. Therefore, the correct answer is C) PbSO4 and Pb3(PO4)2.