Q.101 Chemistry ⭐ 360° Option Elimination Active

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NEET 2020 Chemistry Question 101 Solution

Topic: The p-Block Elements (Group 16) · Official NTA Booklet Code E1

Question

Which of the following oxoacid of sulphur has −O−O− linkage?

✓

Verified Against NTA Final Answer Key

Option (3) : H2S2O8, peroxodisulphuric acid

📚 The p-Block Elements (Group 16) Easy

📋 Given Parameters & Problem Setup

Structural Motif Peroxide linkage (-O-O- bond)

Chemical Family Oxoacids of sulphur

Candidate Compounds H2SO3, H2SO4, H2S2O8, H2S2O7

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The 30-Second Exam Hall Shortcut: ⚡ "PEROXO-disulphuric Acid (H2S2O8, Marshall's Acid) Contains -O-O- Linkage!"

⏱️ 20 seconds

The name itself gives it away: "PEROXO"-disulphuric acid ( $H_2S_2O_8$ , Marshall's acid) contains a peroxy bridge ( $HO_3S-O-O-SO_3H$ ) between the two sulphur atoms! Pyrosulphuric acid ( $H_2S_2O_7$ , oleum) contains an -S-O-S- bridge. Mark H2S2O8 (Option 3) in 5 seconds!

1 Check prefix: "Peroxo" denotes the presence of a peroxide linkage (-O-O-).

2 Formula of Marshall's acid = H2S2O8 (Peroxodisulphuric acid).

3 Structure: HO-SO2-O-O-SO2-OH (contains one -O-O- bond).

4 H2S2O7 (oleum) has S-O-S bond; H2SO4 has no peroxy bond; H2SO3 has S=O, S-OH.

5 Select Option (3) H2S2O8, peroxodisulphuric acid.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Chemistry · The p-Block Elements (Group 16: Oxoacids of Sulphur)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Analyze Chemical Structures of Sulphur Oxoacids

Sulphur forms several oxoacids where sulphur exhibits tetrahedral coordination with oxygen: 1. Sulphurous acid ( $\text{H}_2\text{SO}_3$ ): Contains one $\text{S}=\text{O}$ , two $\text{S}-\text{OH}$ , and one lone pair (oxidation state +4). 2. Sulphuric acid ( $\text{H}_2\text{SO}_4$ ): Contains two $\text{S}=\text{O}$ and two $\text{S}-\text{OH}$ bonds (oxidation state +6).

Step 2

Analyze Pyrosulphuric Acid (Oleum, H2S2O7)

Pyrosulphuric acid ( $\text{H}_2\text{S}_2\text{O}_7$ ) contains two $\text{SO}_3\text{H}$ groups linked through a single oxygen bridge: $\text{HO}-\text{SO}_2-\text{O}-\text{SO}_2-\text{OH}$ . It has an $\text{S}-\text{O}-\text{S}$ linkage, NOT a peroxide linkage.

Step 3

Analyze Peroxodisulphuric Acid (H2S2O8)

Peroxodisulphuric acid (Marshall's acid, $\text{H}_2\text{S}_2\text{O}_8$ ) is formed by joining two sulphuric acid moieties through a peroxy (peroxide) bridge: $\text{HO}-\text{SO}_2-\text{O}-\text{O}-\text{SO}_2-\text{OH}$ The two central oxygen atoms are covalently linked by an $\text{-O-O-}$ single bond, each having an oxidation state of $-1$ , allowing both sulphur atoms to retain the maximum +6 oxidation state.

Step 4

Conclude Correct Option

Therefore, $\text{H}_2\text{S}_2\text{O}_8$ uniquely possesses the $\text{-O-O-}$ peroxide linkage.

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360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 A

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; sulphurous acid contains only S=O and S-OH bonds without any peroxy linkage.

⚠️

Student Fallacy (Why candidates pick this trap): Random choice.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; sulphuric acid contains two S=O and two S-OH bonds, no peroxy linkage.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing standard oxoacid with peroxoacid.

3 C

✓ 100% Correct

Verdict & Scientific Reason:

Factually and structurally exact; Marshall's acid ( $H_2S_2O_8$ ) contains a central peroxy $\text{-O-O-}$ linkage.

💡

Why this is airtight: None; famous oxoacid structure.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; pyrosulphuric acid (oleum) contains an $\text{S}-\text{O}-\text{S}$ bridging linkage, not an $\text{-O-O-}$ linkage.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing pyrosulphuric acid (

H_2S_2O_7

, S-O-S) with peroxodisulphuric acid (

H_2S_2O_8

, S-O-O-S).

⚠️

NTA Trap Alert: Oleum (H2S2O7) vs Marshall's Acid (H2S2O8)

- $H_2S_2O_7$ (Pyrosulphuric acid / Oleum) has an S-O-S linkage. - $H_2S_2O_8$ (Peroxodisulphuric acid / Marshall's acid) has an -O-O- (peroxy) linkage.

🛡️ How to avoid the -1 mark: Look at the oxygen count: 7 oxygens = S-O-S; 8 oxygens = S-O-O-S (Peroxy)!

📖

Core NEET Syllabus Standard

Chemistry · The p-Block Elements Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Oxoacids of Sulphur: Peroxide Linkage (-O-O-) in Peroxodisulphuric Acid (H2S2O8)

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Chemistry Question 101 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "PEROXO-disulphuric Acid (H2S2O8, Marshall's Acid) Contains -O-O- Linkage!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Analyze Chemical Structures of Sulphur Oxoacids

Analyze Pyrosulphuric Acid (Oleum, H2S2O7)

Analyze Peroxodisulphuric Acid (H2S2O8)

Conclude Correct Option

360° Option Elimination Engine Key Feature

NTA Trap Alert: Oleum (H2S2O7) vs Marshall's Acid (H2S2O8)

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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