H2S is less acidic than H2Te because on moving down the group the size of the atom increases and ionization enthalpy decreases. This helps to dissociate the bond easily. So taking the case of H2Te and hence the removal of a hydrogen ion from this compounds becomes easy and acidity is higher due to this. But in case of H2Sthe bond dissociation is less and hence acidity is lower. So H2S is less acidic than H2Te.