Final answer:
H₂O, HF, and NH₃ can behave as both Lewis acids and Lewis bases, while CH₄ cannot.
Step-by-step explanation:
To determine which of the hydrides behave as Lewis acids and Lewis bases, we need to understand the concept of Lewis acids and Lewis bases. Lewis acids are electron pair acceptors, while Lewis bases are electron pair donors.
H₂O can behave as both a Lewis acid and a Lewis base. As a Lewis acid, it can accept an electron pair from a Lewis base. For example, in the reaction H₂O + NH₃ → NH₄⁺ + OH⁻, H₂O accepts an electron pair from NH₃. As a Lewis base, it can donate an electron pair to a Lewis acid. For example, in the reaction H₂O + BF₃ → H₃O⁺ + BF₃⁻, H₂O donates an electron pair to BF₃.
HF can also behave as both a Lewis acid and a Lewis base. As a Lewis acid, it can accept an electron pair from a Lewis base. For example, in the reaction HF + NH₃ → NH₄⁺ + F⁻, HF accepts an electron pair from NH₃. As a Lewis base, it can donate an electron pair to a Lewis acid. For example, in the reaction HF + BF₃ → H₃O⁺ + BF₄⁻, HF donates an electron pair to BF₃.
NH₃ can behave as a Lewis base. As a Lewis base, it can donate an electron pair to a Lewis acid. For example, in the reaction NH₃ + BF₃ → NH₄⁺ + F⁻, NH₃ donates an electron pair to BF₃.
CH₄ does not have the ability to behave as a Lewis acid or a Lewis base because it lacks the necessary electron lone pairs for donation or acceptance.