Answer:
Zinc ions (Zn²+) do not decompose when heated, but hydrated zinc salts can lose water (H2O) molecules when heated, forming anhydrous salts.
Lead ions (Pb²+) can decompose when a lot of heat is added, producing lead oxide (PbO) and oxygen (O2) gas.
Iron ions (Fe³+) can undergo different reactions depending on the conditions. FeCl₃ (hydrated iron (III) chloride), for example can decompose when heated to produce anhydrous FeCl₃ and water vapor. But if Fe(OH)₃ (hydrated iron(III) hydroxide), is heated strongly, it decomposes to form Fe₂O₃ (iron oxide) and water vapor.
The behavior of hydrated salts when heated can vary depending on the specific compound but generally, hydrated salts lose their water (H2O) molecules on heating and become anhydrous salts.