Which of the following is amphoteric substance?

Explanation

An amphoteric substance has the ability to act as both an acid and a base. Water (H₂O) is a classic example of an amphoteric substance because it can donate a proton, forming hydroxide ions (OH⁻), or accept a proton, forming hydronium ions (H₃O⁺). Therefore, it can behave as either an acid or a base depending on the reaction conditions. In contrast, Na₂O is a basic oxide, H₂CO₃ is primarily an acid, and NH₄OH is a weak base, none of which exhibit the dual functionality required to be considered amphoteric.