Which of the following compounds is thermodynamically unstable?

All of the hydrides given belongs to the same group (Group 16) of the periodic table. On moving down the group, atomic size increases. This means the bond length between hydrogen and the group 16 elements also increases. With the increase in bond length the bond strength decreases. This means that the bond dissociation energy of these hydrides also decreases down the group. Thus, the hydride of the element residing at the bottom of the group will be least stable and it can dissociate easily. In group 16, the elements from top to bottom are: O, S, Se. Hence the order of stability for these hydr