Question

Why is H2S more acidic than H2O ?

Answer 1

 The S-H bond is weaker than the O-H bond, meaning that H2S more easily donates a proton and is therefore more acidic. 

Answer 2

$\huge\mathfrak{Answer}$

S is much larger atom than O, so the H–S bond is much longer and weaker than H–O;

hence H2O is weaker acid than H2S.

HF is stronger than H2S because the small F- ion bonds more strongly to the water molecules than does the larger HS- ion.