Aluminum oxide is incompatible with which of the following?

• A. Nitric acid (red fuming)
• B. Water
• C. Copper
• D. Acetylene

Answer: (A)

The key idea is that very strong oxidizing acids can attack materials you might think are fairly inert, including metal oxides like aluminum oxide. Red fuming nitric acid is an extremely powerful oxidizer and nitrating agent. In contact with aluminum oxide, it can drive oxidation reactions that disrupt the oxide surface, potentially dissolving the oxide to form aluminum nitrate and nitrogen oxides and releasing heat. That makes this combination incompatible and potentially hazardous.

Water is harmless to aluminum oxide and won’t react under ordinary conditions. Copper and acetylene don’t have a reactive incompatibility with aluminum oxide in typical storage or handling scenarios, so they’re not flagged as incompatibilities here.