Which statement is correct for acids?

Correct answer: They can produce carbon dioxide from metal carbonates

Acids react with metal carbonates to form a salt, water, and carbon dioxide: acid + carbonate → salt + H₂O + CO₂. This reaction makes option A correct. Acids generally turn blue litmus red, so option B reverses the indicator change. In aqueous solution acids produce ions, especially hydrogen or hydronium ions, which rejects option C. They do not produce oxygen with all metals, so D is also false.