Final answer:
NO2 is the most acidic oxide among the given options.
Step-by-step explanation:
The most acidic oxide among the options given is NO2.
Acidity of oxides depends on the presence of hydrogen ions (H+). When oxides react with water, they form acids which have hydrogen ions. In NO2, nitrogen (N) is bonded to two oxygen (O) atoms, and it readily reacts with water to form nitric acid (HNO3), releasing H+ ions, making it the most acidic oxide among the given options.
On the other hand, CaO, Al2O3, BaO, and SO2 do not readily produce hydrogen ions when they react with water, so they are less acidic compared to NO2.
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