Answer the question on the basis of the passage given below:
Oxides formed by \(p\)- block elements are acidic, basic and neutral. Also, elements of \(p\)-block form different acids.
\(HOCl < HOClO < HOClO_2 < HOClO_3\) It is correct order for which of the following?
A. increasing acidic strength
B. decreasing order of oxidising power
C. increasing order of oxidising power
D. increasing basic strength
Choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A and C only
Note 1: The given answer is as per the official NTA Answer Key. However, the correct answer should be Option (1) A and B only, as explained below.
The four acids are the oxoacids of chlorine in the +1, +3, +5 and +7 states: HOCl (hypochlorous), HOClO = \( \ce{HClO2} \) (chlorous), \( \ce{HOClO2} \) = \( \ce{HClO3} \) (chloric) and \( \ce{HOClO3} \) = \( \ce{HClO4} \) (perchloric). The more O atoms on chlorine, the more the negative charge of the anion is spread out, so the anion is more stable.
(A) increasing acidic strength — Correct. Each extra O atom on chlorine pulls electron density from the O–H bond, and the anion becomes more stable (\( \ce{ClO4^-} \) is the most stable). So acid strength rises from HOCl to \( \ce{HClO4} \).
(B) decreasing order of oxidising power — Correct. HOCl is the strongest oxidising agent of the four and \( \ce{HClO4} \) the weakest: the more stable the anion, the less readily it gives up oxygen.
Oxidising power: HOCl > \( \ce{HClO2} \) > \( \ce{HClO3} \) > \( \ce{HClO4} \)
(C) increasing order of oxidising power — As per NTA it is correct. However, this statement is not correct. The oxidising power falls from HOCl to \( \ce{HClO4} \), because the anion becomes more stable as more O atoms share the charge. So the given order is not one of increasing oxidising power, and the correct combination is A and B, i.e. Option (1).
(D) increasing basic strength — Incorrect. These are acids, and their acidic strength increases along the order.
Note 2: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.