Explanation

(b)
Theacidic nature increases from H_{2}O to H_{2}Te. The increase in acidic character of hydrides on moving down the group may be explained in terms of bond length of H—M bond, larger is bond length lesser is bond energy and thus easier is ionization of H—M bond or easier is proton donor nature. Hence,
H_{2}O < H_{2}S < H_{2}Se < H_{2}Te