Based on general solubility rules, which of the following compounds is...
CASH-N-GIA is a mnemonic for solubility rules. Chlorates, Acetates, Sulfates, Halides (not Fluorides), Nitrates, Group I metals, Ammonium. These compounds are generally soluble.
Lead chloride, PbCl2 is a halide or chloride, but it is one of the exceptions which include mercury Hg22+, silver Ag+, and lead Pb2+. Think HAPpy.
Calcium sulfate, CaSO4, is a sulfate, but it is one of the exceptions which include the HAPpy group from above, but also CBS for the Group II metals, calcium Ca2+, barium Ba2+, and strontium Sr2+.
The hydroxides are not part of CASHNGIA and should be considered insoluble. The expected exceptions are the Group I metals and ammonium. Aluminum hydroxide, Al(OH)3, therefore, is considered insoluble.
The chromates are also not part of CASHNGIA, but cesium Cs is a Group I metal, and therefore, caesium chromate, Cs2CrO4 is considered soluble.
The correct answer is Cs2CrO4.