Q.81 Chemistry ⭐ 360° Option Elimination Active

Vault ↗

NEET 2026 Chemistry Question 81 Solution

Topic: Redox Reactions · Official NTA Booklet Code 50

Question

The correct decreasing order of oxidation state of the underlined atom in each molecule is

✓

Verified Against NTA Final Answer Key

Option (2) : N₂O₅ > Al₂O₃ > H₂S

📚 Redox Reactions Easy

📋 Given Parameters & Problem Setup

Requirement Correct decreasing order of oxidation state of the underlined atom

Option 2 Molecules N₂O₅ (N), Al₂O₃ (Al), H₂S (S)

⚡

The 30-Second Exam Hall Shortcut: ⚡ Fast Oxidation Number Scan

⏱️ Save ~45 seconds

Calculate oxidation numbers directly: Option 2 gives +5 > +3 > -2!

1 Check Option 1: P₄O₁₀ (P = +5), SO₃ (S = +6), H₂O (O = -2). +5 is NOT > +6 -> False!

2 Check Option 2: N₂O₅ (N = +5), Al₂O₃ (Al = +3), H₂S (S = -2). +5 > +3 > -2 is strictly decreasing -> TRUE!

3 Check Option 3: PbO₂ (Pb = +4), N₂O₃ (N = +3), SO₃ (S = +6). +3 is NOT > +6 -> False!

4 Check Option 4: P₄O₆ (P = +3), Cl₂O₇ (Cl = +7). +3 is NOT > +7 -> False!

5 Option (2) is unequivocally correct in 15 seconds!

🛡️

Why You Can 100% Trust This Shortcut: Standard oxidation number rules: Oxygen is -2, Hydrogen is +1, Group 13 Al is +3.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Determine Oxidation States in Option (2)

1. In N₂O₅: 2x + 5(-2) = 0 ⇒ 2x = +10 ⇒ x = +5 for Nitrogen. 2. In Al₂O₃: 2x + 3(-2) = 0 ⇒ 2x = +6 ⇒ x = +3 for Aluminium. 3. In H₂S: 2(+1) + x = 0 ⇒ x = -2 for Sulfur.

\text{O.S. in Option (2): } \text{N}(+5) > \text{Al}(+3) > \text{S}(-2)

• The values +5, +3, -2 follow a strictly decreasing sequence.

Step 2

Verify Invalidation of Option (1)

In P₄O₁₀, 4x + 10(-2) = 0 ⇒ x = +5. In SO₃, x + 3(-2) = 0 ⇒ x = +6. In H₂O, 2(+1) + x = 0 ⇒ x = -2. The sequence +5, +6, -2 is NOT decreasing because +5 < +6.

+5 < +6 \implies \text{Option (1) is invalid}

• Violates decreasing order.

Step 3

Verify Invalidation of Options (3) and (4)

In Option (3): PbO₂ (+4), N₂O₃ (+3), SO₃ (+6). Here +3 < +6 (invalid). In Option (4): P₄O₆ (+3), Cl₂O₇ (+7), AlH₃ (+3). Here +3 < +7 (invalid).

\text{Only Option (2) satisfies strictly decreasing oxidation states}

• Matches Option (2).

⭐

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. P is +5 and S is +6; +5 is less than +6.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming phosphorus with 10 oxygens must have a higher oxidation state than sulfur with 3 oxygens.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

Flawless: N is +5, Al is +3, S is -2, representing a strictly decreasing order (+5 > +3 > -2).

💡

Why this is airtight: None; simple and rigorous arithmetic.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. SO₃ has S in +6, which is higher than +3 in N₂O₃.

⚠️

Student Fallacy (Why candidates pick this trap): Failing to calculate sulfur's oxidation state in SO₃.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Cl₂O₇ has Cl in +7, which is greater than +3 in P₄O₆.

⚠️

Student Fallacy (Why candidates pick this trap): Overlooking chlorine's maximum +7 state in Cl₂O₇.

⚠️

NTA Trap Alert: Confusing Number of Oxygen Atoms with Oxidation State

Students frequently look at subscripts: "P₄O₁₀ has 10 oxygens, so it must be higher than SO₃ with 3 oxygens!" But each P in P₄O₁₀ is only +5, while S in SO₃ is +6!

🛡️ How to avoid the -1 mark: Always divide total oxygen formal charge by the number of central atoms: 20/4 = +5, whereas 6/1 = +6.

📖

Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Redox Reactions Standard Benchmark

Core Scientific Principle Tested:

"Oxidation numbers are assigned per atom based on standard electronegativity rules."

Syllabus Focus: Concept of oxidation number and calculation rules

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Divide total negative by central count: +5, then +3, then -2 on the mount!

Ready to attempt under real exam pressure?

Test your speed and accuracy in the authentic 180-minute timed NTA simulator.

Launch NEET 2026 CBT Test →

← Previous (Q.80) All Chemistry Questions Grid Next (Q.82) →

Spotted a mistake in this solution? Report an error ([email protected])

⚖️ Legal & Fair Dealing Notice: Sourced from publicly released NEET 2026 question papers and NEET answer keys for private study, research, and non-commercial educational practice under Fair Dealing (Section 52(1)(a) of the Indian Copyright Act, 1957). Not affiliated with or endorsed by NTA or NMC.

NEET 2026 Chemistry Question 81 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Fast Oxidation Number Scan

Step-by-Step Rigorous Workflow & Mathematical Proof

Determine Oxidation States in Option (2)

Verify Invalidation of Option (1)

Verify Invalidation of Options (3) and (4)

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Number of Oxygen Atoms with Oxidation State

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Redox Reactions

Oxidation States of Underlined Elements in KO₂, H₂O₂ and H₂SO₄

Identification of Non-Redox (Double Displacement) Reactions

Balancing Redox Reactions by Ion-Electron Method in Acidic Medium

Classification of Redox Reactions: Metal Displacement

Solve 4 NEET Questions a Day — One per Subject