(1) The residents of Saudi Arabia belong to the Arab nation, and the main language is Arabic; Saudi Arabia's national average income is very high, mainly relying on the exploitation and export of a large number of oil resources.

(2) Riyadh, Doha and other cities have tropical desert climate, which is very hot in summer, so Riyadh and Doha often avoid holding large-scale sports events in summer;

(3) Iraq is a world-famous date palm producer. The favorable natural conditions for planting date palms in this country are sufficient light and heat, large temperature difference between day and night, favorable accumulation of organic matter, sufficient irrigation water, flat terrain and fertile soil.

So the answer is:

(1) Arabia; Oil;

(2) It has a tropical desert climate and is very hot in summer.

(3) Sufficient light and heat and large temperature difference between day and night are conducive to the accumulation of organic matter, sufficient irrigation water, flat terrain and fertile soil.