Can we give iron rusting as an example of oxidation? How essential is water in chemical weathering processes? Can chemical weathering processes dominate in water scarce hot deserts?

Yes iron rusting is an example of chemical oxidation.

In chemical weathering process in rocks like feldspar, granite. When water comes in contact with these rocks, a chemical reaction takes places which erode the rocks thereby weakening it.

No it can’t dominate in water scarce hot deserts.