Oxygen is more electronegative than sulphur, yet ${\mathrm{H}}_2\mathrm{ }\mathrm{S}$ is acidic while ${\mathrm{H}}_2\mathrm{O}$ is neutral. This is because

${\mathrm{H}}_2\mathrm{ }\mathrm{S}$ is acidic while ${\mathrm{H}}_2\mathrm{O}$ is neutral because:

- Size of $S$ is large which makes $\mathrm{H}-\mathrm{S}$ bond weaker than $\text{H-O}$ bond. Thus it can give a proton more easily.

- ${\mathrm{H}}_2\mathrm{O}$ can form strong $\mathrm{H}$-bonding.