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

**Step 1: Understand what pK_a measures**
pK_a is defined as the negative base‑10 logarithm of the acid dissociation constant (K_a):
$-log$₁₀(K_a). A lower pK_a means a stronger acid (larger K_a).

**Step 2: Look up the experimental pK_a values**
For the hydrides of group 16 (oxygen, sulfur, selenium, tellurium) the measured pK_a values in water are approximately:
‑ H₂O: pK_a ≈ 15.7
‑ H₂S: pK_a ≈ 7.0
‑ H₂Se: pK_a ≈ 3.9
‑ H₂Te: pK_a ≈ 2.6

**Step 3: Arrange the compounds in order of increasing pK_a**
Since pK_a increases from a lower value to a higher value, the correct ascending sequence is:
H₂Te (2.6) < H₂Se (3.9) < H₂S (7.0) < H₂O (15.7).

**Step 4: Compare with the given arrangement**
The statement in the option lists the series as:
H₂O < H₂S < H₂Se < H₂Te.

**Step 5: Identify the inconsistency**
In this sequence, the pK_a values are actually decreasing (15.7 → 7.0 → 3.9 → 2.6), which corresponds to **increasing acidity**, not increasing pK_a. Therefore the arrangement does **not** follow the property “Increasing pK_a values”.

**Conclusion**
The option “H₂O < H₂S < H₂Se < H₂Te : Increasing pK_a values” is the one where the given sequence is not strictly according to the indicated property.