In this reaction, hydrogen selenide (H2Se) acts as the acid, while water (H2O) functions as the base. The conjugate acid formed from this reaction is the hydronium ion (H3O+), and the conjugate base is the selenide ion (SeH–). H2Se donates a proton (H+) to water, which corresponds to the definition of an acid, while water, which accepts the proton, is identified as the base.
From a periodic table perspective, hydrogen selenide is part of the group of hydrides, where as you move down the group (from H2O to H2Se), the acidic character increases due to the larger size and lower electronegativity of selenium compared to oxygen. This trend supports H2Se's behavior as a stronger acid than water, while water remains a stable, common base.