Iron is widely distributed in nature, but its discovery and utilization are much later than gold and copper.

(1) The condition of iron rusting is that it reacts with water and oxygen in the air, and it is easy to rust in the humid weather in the south. The desert is dry and does not rust easily.

So the answer is: the weather in the south is humid and meets the conditions of rust; The weather in desert area is dry and it is not easy to rust.

(2) rust is soft and porous, which will make iron rust faster; Aluminum reacts with oxygen to form a dense alumina film on its surface, which prevents further oxidation of aluminum, so the corrosion resistance of aluminum is stronger than that of iron.

So the answer is: aluminum reacts with oxygen to form a dense alumina film on its surface, thus preventing further oxidation of aluminum.

(3)①X can react with dilute HCl, but Y can't, so it is inferred that the activity of X is greater than Y; ② It is inferred from "both Y and Z are immersed in AgNO _ 3 solution, Ag precipitates on Y surface, and Z remains unchanged" that the activity of Y is greater than that of Ag, while that of Z is less than that of Ag. To sum up, it is X > Y > Ag > Z, and the selected y should be between h and Ag, such as Cu and Hg.

So the answer is: ① x > y > ag > z? ② Copper +2 nitric acid ═2Ag+Cu(NO 3) 2.