You are absolutely right! All three of these substances are amphoteric. Here's why:

* NH₃ (Ammonia):

* As a base: NH₃ + H⁺ → NH₄⁺ (accepts a proton)

* As an acid: NH₃ + H₂O → NH₂⁻ + H₃O⁺ (donates a proton)

* CH₃COOH (Acetic acid):

* As an acid: CH₃COOH + H₂O → CH₃COO⁻ + H₃O⁺ (donates a proton)

* As a base: CH₃COOH + H⁺ → CH₃COOH₂⁺ (accepts a proton)

* H₂O (Water):

* As an acid: H₂O + H₂O → OH⁻ + H₃O⁺ (donates a proton)

* As a base: H₂O + H⁺ → H₃O⁺ (accepts a proton)

Key takeaway: A substance is amphoteric if it can act as both an acid (donate a proton) and a base (accept a proton).