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Question:

Which is the correct thermal stability order for H₂E (E = O, S, Se, Te, and Po)?

H₂S < H₂O < H₂Se < H₂Te < H₂Po

H₂O < H₂S < H₂Se < H₂Te < H₂Po

H₂Po < H₂Te < H₂Se < H₂S < H₂O

H₂Se < H₂Te < H₂Po < H₂O < H₂S

Solution:

Correct option is C. H₂Po < H₂Te < H₂Se < H₂S < H₂O
On going down the group, the thermal stability order for H₂E decreases because the H−E bond energy decreases. Hence, the order of stability would be H₂Po < H₂Te < H₂Se < H₂S < H₂O