Final answer:
B. Ag, Cd, Zn, Al. The four fixed charge metals from the provided list are silver (Ag), cadmium (Cd), zinc (Zn), and aluminum (Al), as they form cations with a constant charge.
Step-by-step explanation:
The question asks which four elements from the given list are fixed charge metals. Fixed charge metals are elements that form cations with a constant positive charge that does not vary. Based on the information provided, we can determine that silver (Ag) forms the cation Ag+, zinc (Zn) forms the cation Zn2+, cadmium (Cd) forms the cation Cd2+, and aluminum (Al) forms the cation Al3+.
These metals form cations with charges that do not change, unlike transition metals which can have multiple possible charges. Hence, the four fixed charge metals are Ag, Cd, Zn, and Al.