Question

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

• A. CO₂ < SiO₂ < SnO₂ < PbO₂ :Increasing oxidizing power
• B. HF < HCl< HBr < HI:Increasing acidic strength
• C. H₂O < H₂S< H₂Se < H₂Te:Increasing pKa values
• D. NH₃ < PH₃< AsH₃ < SbH₃:Increasing acidic character

Answer 1

The Correct Option is C

To solve this question, we need to analyze each of the given sequences against their respective properties and determine which sequence is not ordered correctly. Let's evaluate each option: 

1. CO₂ < SiO₂ < SnO₂ < PbO₂: Increasing oxidizing power
   As we move from CO₂ to PbO₂, the oxidizing power generally increases. This is because lead (Pb) as PbO₂ is a strong oxidizing agent compared to carbon (CO₂). Thus, this sequence is correct.
2. HF < HCl < HBr < HI: Increasing acidic strength
   The acidic strength of hydrogen halides increases from HF to HI. This is due to the decreasing bond strength and increasing size of the halogen, making HI the strongest acid among them. Therefore, this sequence is also correct.
3. H₂O < H₂S < H₂Se < H₂Te: Increasing pKa values
   As we move down the group from H₂O to H₂Te, the acid strength increases, which means the pKa value should decrease. Therefore, the correct sequence should be in decreasing order of pKa values, not increasing. This means this particular arrangement does not match the indicated property.
4. NH₃ < PH₃ < AsH₃ < SbH₃: Increasing acidic character
   The acidic character of hydrides increases from NH₃ to SbH_{3>. This is due to the decreasing bond strength and increasing size along with the group, making SbH3 more acidic than NH3. Thus, this sequence is correct.}

Based on the analysis above, the incorrect sequence concerning the indicated property is:

H₂O < H₂S < H₂Se < H₂Te: Increasing pKa values