Q.85 Chemistry ⭐ 360° Option Elimination Active
NEET 2026 Chemistry Question 85 Solution
Topic: The d- and f-Block Elements · Official NTA Booklet Code 50
Question
The green paramagnetic species formed by heating KMnO, at 513 K is
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Verified Against NTA Final Answer Key
Option (1) : K₂MnO₄
📚 The d- and f-Block Elements Easy
📋 Given Parameters & Problem Setup
Reactant KMnO₄ (Potassium permanganate, dark purple, diamagnetic Mn⁺⁷)
Reaction Condition Heating at 513 K (240 °C)
Characteristics Green, paramagnetic species formed
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⏱️ Save ~45 seconds The 30-Second Exam Hall Shortcut: ⚡ The Green Manganate Fingerprint
KMnO₄ heated at 513 K decomposes to GREEN Potassium Manganate (K₂MnO₄)!
1 Recall thermal decomposition of KMnO₄: 2 KMnO₄ → K₂MnO₄ + MnO₂ + O₂.
2 K₂MnO₄ (potassium manganate) contains the manganate ion [MnO₄]²⁻.
3 Manganese is in the +6 oxidation state (d¹ configuration), which has ONE unpaired electron (paramagnetic) and exhibits a characteristic dark GREEN color!
4 Option (1) is K₂MnO₄ -> Instant selection in 5 seconds!
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Why You Can 100% Trust This Shortcut: NCERT d- and f-Block Elements verbatim: Potassium permanganate on heating decomposes at 513 K to give potassium manganate (K₂MnO₄), manganese dioxide, and oxygen.
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
State the Chemical Reaction for Thermal Decomposition of KMnO₄
Potassium permanganate decomposes upon heating above 513 K (240 °C) in a solid-state disproportionation/decomposition reaction:
- • Products are potassium manganate (K₂MnO₄), black manganese dioxide (MnO₂), and oxygen gas (O₂).
Step 2
Analyze the Color and Magnetism of Potassium Manganate (K₂MnO₄)
1. Oxidation state: In K₂MnO₄, potassium is +1 and oxygen is -2. 2(+1) + x + 4(-2) = 0 ⇒ x = +6. 2. Electronic configuration: Mn (Z = 25) is [Ar] 3d⁵ 4s². Mn(VI) is [Ar] 3d¹. 3. Magnetism: The single unpaired electron in the 3d orbital makes the manganate ion [MnO₄]²⁻ PARAMAGNETIC (μ ≈ 1.73 BM). 4. Color: The tetraoxo anion [MnO₄]²⁻ absorbs light via ligand-to-metal charge transfer (LMCT) and d-d transitions, appearing intensely DARK GREEN.
- • Color: Green.
- • Magnetism: Paramagnetic.
- • Formula: K₂MnO₄.
Step 3
Contrast with KMnO₄ Precursor
In contrast, KMnO₄ has manganese in the +7 oxidation state (3d⁰), which has no unpaired d-electrons and is diamagnetic (dark purple due to LMCT).
- • Matches Option (1).
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 A
✓ 100% Correct Verdict & Scientific Reason:
Exact match with textbook thermal decomposition: K₂MnO₄ is green and paramagnetic (3d¹).
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Why this is airtight: None; direct factual recall.
2 B
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Hausmannite (Mn₃O₄) is formed by heating MnO₂ at much higher temperatures (> 1000 °C), not by heating KMnO₄ at 513 K.
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Student Fallacy (Why candidates pick this trap): Confusing high-temperature oxide conversions.
3 C
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Manganous oxide (MnO) is a green-gray basic oxide formed by reducing MnO₂ with H₂, not thermal decomposition of KMnO₄.
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Student Fallacy (Why candidates pick this trap): Associating the color green with MnO instead of the manganate salt.
4 D
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Potassium superoxide (KO₂) is an orange solid formed by burning potassium in excess oxygen, not a product of KMnO₄ decomposition.
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Student Fallacy (Why candidates pick this trap): Random alkali metal superoxide guess.
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NTA Trap Alert: Confusing Manganate (Green, K₂MnO₄) with Permanganate (Purple, KMnO₄)
Students frequently confuse potassium manganate (K₂MnO₄, Mn⁺⁶, green) with potassium permanganate (KMnO₄, Mn⁺⁷, purple). Heating KMnO₄ gives K₂MnO₄!
🛡️ How to avoid the -1 mark: Permanganate = Purple (Mn⁺⁷); Manganate = Green (Mn⁺⁶).
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Core NEET Syllabus Standard
NEET Chemistry Core Syllabus · The d- and f-Block Elements Standard Benchmark
Core Scientific Principle Tested:
"2 KMnO₄ decomposes thermally at 513 K into green paramagnetic K₂MnO₄, MnO₂, and O₂."
Syllabus Focus: Compounds of manganese - Potassium permanganate and potassium manganate
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗
Purple Permanganate heated to 513 K turns Green Manganate all the way!
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