Q.131 Chemistry ⭐ 360° Option Elimination Active

NEET 2020 Chemistry Question 131 Solution

Topic: Classification of Elements and Periodicity in Properties · Official NTA Booklet Code E1

Question

Match the following: Oxide Nature (a) CO (i) Basic (b) BaO (ii) Neutral (c) Al2O3 (iii) Acidic (d) Cl2O7 (iv) Amphoteric Which of the following is correct option? (a) (b) (c) (d)

(1)(i) (ii) (iii) (iv)
(2)(ii) (i) (iv) (iii)
(3)(iii) (iv) (i) (ii)
(4)(iv) (iii) (ii) (i)

✓

Verified Against NTA Final Answer Key

Option (2) : (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)

📚 Classification of Elements and Periodicity in Properties Easy

📋 Given Parameters & Problem Setup

Column I (Oxides) (a) CO, (b) BaO, (c) Al2O3, (d) Cl2O7

Column II (Nature) (i) Basic, (ii) Neutral, (iii) Acidic, (iv) Amphoteric

⚡

The 30-Second Exam Hall Shortcut: ⚡ "CO = Neutral; BaO = Basic; Al2O3 = Amphoteric; Cl2O7 = Strongly Acidic!"

⏱️ 20 seconds

CO is a neutral oxide (along with NO and N2O; a->ii). BaO is an alkaline earth metal oxide, hence strongly basic (b->i). Al2O3 reacts with both acids and bases, hence amphoteric (c->iv). Cl2O7 is a non-metal oxide in maximum +7 oxidation state, hence strongly acidic (d->iii). Match gives (ii), (i), (iv), (iii) -> Option 2 in 5 seconds!

1 CO is neutral -> (a)-(ii).

2 BaO is an electropositive alkaline earth basic oxide -> (b)-(i).

3 Al2O3 is amphoteric (reacts with HCl and NaOH) -> (c)-(iv).

4 Cl2O7 is acidic (forms perchloric acid HClO4 with water) -> (d)-(iii).

5 Resulting combination: (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii) -> Option 2.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Chemistry · Classification of Elements and Periodicity in Properties (Periodic Trends: Chemical Reactivity of Oxides)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Match Carbon Monoxide (CO)

Carbon monoxide ( $\text{CO}$ ) is neutral; it shows neither acidic nor basic properties and does not form salts with acids or bases (other neutral oxides are $\text{NO}$ and $\text{N}_2\text{O}$ ). Thus, (a) matches (ii).

Step 2

Match Barium Oxide (BaO)

Barium is a highly electropositive alkaline earth metal (Group 2). Its oxide, $\text{BaO}$ , dissolves in water to form the strong base barium hydroxide ( $\text{Ba(OH)}_2$ ) and reacts vigorously with acids. Thus, (b) matches (i).

Step 3

Match Aluminium Oxide (Al2O3)

$\text{Al}_2\text{O}_3$ exhibits both acidic and basic characteristics, dissolving in hydrochloric acid to form aluminium chloride and in sodium hydroxide to form sodium aluminate ( $\text{Na[Al(OH)}_4]$ ). Thus, (c) matches (iv) Amphoteric.

Step 4

Match Dichlorine Heptoxide (Cl2O7)

Chlorine is a strongly electronegative halogen in its highest oxidation state (+7). $\text{Cl}_2\text{O}_7$ dissolves in water to form perchloric acid ( $\text{HClO}_4$ ), one of the strongest inorganic acids. Thus, (d) matches (iii) Acidic.

⭐

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; claims CO is basic and BaO is neutral.

⚠️

Student Fallacy (Why candidates pick this trap): Swapping basic and neutral.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

Accurate pairing across all four chemical oxide types.

💡

Why this is airtight: None; textbook acid-base oxide classification.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; misassigns CO to acidic and BaO to amphoteric.

⚠️

Student Fallacy (Why candidates pick this trap): Arbitrary matching.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; claims CO is amphoteric and Cl2O7 is basic.

⚠️

Student Fallacy (Why candidates pick this trap): Completely inverted assignments.

⚠️

NTA Trap Alert: Neutral Oxides in NCERT

Memorize the four common NEUTRAL oxides: CO, NO, N2O, and H2O! Non-metal oxides with low oxidation states are neutral, while high oxidation state oxides like Cl2O7 are strongly acidic.

🛡️ How to avoid the -1 mark: Remember: CO = Neutral; Al2O3 = Amphoteric!

📖

Core NEET Syllabus Standard

Chemistry · Classification of Elements and Periodicity in Properties Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Acid-Base Character of Oxides: Neutral, Basic, Amphoteric and Acidic Oxides

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Chemistry Question 131 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "CO = Neutral; BaO = Basic; Al2O3 = Amphoteric; Cl2O7 = Strongly Acidic!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Match Carbon Monoxide (CO)

Match Barium Oxide (BaO)

Match Aluminium Oxide (Al2O3)

Match Dichlorine Heptoxide (Cl2O7)

360° Option Elimination Engine Key Feature

NTA Trap Alert: Neutral Oxides in NCERT

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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