In which one of the following arrangements the given sequence is not strictly according to the properties indicated against it ?

The correct option is: H₂O < H₂S < H₂Se < H₂Te (increasing acid strength / or any property that is not strictly according to this sequence depending on the standard properties indicated in chemistry questions, but let's explain why this sequence is incorrect for the typical property associated with it, or clarify the trends).

Let's analyze the properties of hydrides of Group 16 elements (oxygen family: H₂O, H₂S, H₂Se, H₂Te) and Group 15/17 hydrides:
1. Acid strength of halogen acids: HF < HCl < HBr < HI. This trend is correct because bond dissociation enthalpy decreases as size increases from F to I, making it easier to release H⁺ ions.
2. Acid strength of Group 16 hydrides: H₂O < H₂S < H₂Se < H₂Te. As the size of the central atom increases down the group, the E-H bond strength decreases (where E = O, S, Se, Te), making it easier to release H⁺. Thus, acid strength increases down the group. Similarly, thermal stability decreases: H₂O > H₂S > H₂Se > H₂Te.
However, if we look at the boiling point trend, it is not strictly increasing down the group because of strong intermolecular hydrogen bonding in water. The order of boiling points is:
$H_{2}S<H_{2}Se<H_{2}Te<H_{2}O$.
Therefore, the sequence H₂O < H₂S < H₂Se < H₂Te is not strictly according to properties like boiling point or thermal stability (where H₂O should be highest).