Question

Hydrogen selenide (H2Se) reacts with water according to the following equation.

Answer 1

H2Se is the acid as it is donating H+ to H2O and forming SeH- (which is conjugate base).

H2O is the base since it’s receiving H+ from H2Se to form H3O+ (which is the conjugate acid)

Se is in the same group as O but is in different period which means Se has higher radius compred to O. this led to H-O bond being stronger than H-Se bond and H-Se bond which in turn makes it easier for H2Se to donate H to H2O