Q.68 Chemistry ⭐ 360° Option Elimination Active

NEET 2025 Chemistry Question 68 Solution

Topic: Some Basic Concepts of Chemistry · Official NTA Booklet Code 45

Question

Among the following, choose the ones with equal number of atoms. A. 212 g of Na₂CO₃(s) [molar mass = 106 g] B. 248 g of Na₂O(s) [molar mass = 62 g] C. 240 g of NaOH(s) [molar mass = 40 g] D. 12 g of H₂(g) [molar mass = 2 g] E. 220 g of CO₂(g) [molar mass = 44 g] Choose the correct answer from the options given below:

✓

Verified Against NTA Final Answer Key

Option (2) : A, B, and D only

📚 Some Basic Concepts of Chemistry Easy

📋 Given Parameters & Problem Setup

Substance A 212 g of Na₂CO₃(s) [molar mass = 106 g]

Substance B 248 g of Na₂O(s) [molar mass = 62 g]

Substance C 240 g of NaOH(s) [molar mass = 40 g]

Substance D 12 g of H₂(g) [molar mass = 2 g]

Substance E 220 g of CO₂(g) [molar mass = 44 g]

⚡

The 30-Second Exam Hall Shortcut: ⚡ Moles × Atomicity Calculation Shortcut

⏱️ Save ~40 seconds

Calculate (Mass / Molar Mass) × Atoms per molecule: A = (212/106) × 6 = 12 N_A. B = (248/62) × 3 = 12 N_A. C = (240/40) × 3 = 18 N_A. D = (12/2) × 2 = 12 N_A. E = (220/44) × 3 = 15 N_A! A, B, and D all equal 12 N_A!

1 A (Na₂CO₃): n = 212 / 106 = 2 moles. Atomicity = 2(Na) + 1(C) + 3(O) = 6. Total atoms = 2 × 6 = 12 N_A.

2 B (Na₂O): n = 248 / 62 = 4 moles. Atomicity = 2(Na) + 1(O) = 3. Total atoms = 4 × 3 = 12 N_A.

3 C (NaOH): n = 240 / 40 = 6 moles. Atomicity = 1(Na) + 1(O) + 1(H) = 3. Total atoms = 6 × 3 = 18 N_A.

4 D (H₂): n = 12 / 2 = 6 moles. Atomicity = 2(H) = 2. Total atoms = 6 × 2 = 12 N_A.

5 E (CO₂): n = 220 / 44 = 5 moles. Atomicity = 1(C) + 2(O) = 3. Total atoms = 5 × 3 = 15 N_A.

6 Equal atom count: A, B, and D all have exactly 12 moles of atoms (12 N_A)!

7 Match Option (2) in under 20 seconds!

🛡️

Why You Can 100% Trust This Shortcut: Mole Concept and Stoichiometric Calculations (NCERT Chemistry · Some Basic Concepts of Chemistry).

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Formulate Equation for Total Number of Atoms

For any substance of mass m, molar mass M, and atomicity N_{atoms} (atoms per formula unit):

\text{Total Atoms} = n \times N_{atoms} \times N_A = \left(\frac{m}{M}\right) \times N_{atoms} \times N_A

• Two samples have an equal number of atoms if their product n × N_{atoms} is identical.

Step 2

Calculate Atoms for Substances A, B, and C

Compute the moles of atoms for the solid ionic compounds:

A: \frac{212}{106} \times 6 = 2 \times 6 = 12\text{ moles of atoms} \quad (12 N_A)

• B: (248 / 62) × 3 = 4 × 3 = 12 moles of atoms (12 N_A).
• C: (240 / 40) × 3 = 6 × 3 = 18 moles of atoms (18 N_A).

Step 3

Calculate Atoms for Substances D and E and Match

Compute the moles of atoms for the gaseous species:

D: \frac{12}{2} \times 2 = 6 \times 2 = 12\text{ moles of atoms} \quad (12 N_A)

• E: (220 / 44) × 3 = 5 × 3 = 15 moles of atoms (15 N_A).
• Comparing values: A = 12 N_A, B = 12 N_A, D = 12 N_A.
• Therefore, A, B, and D have equal numbers of atoms, matching 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. C has 18 N_A atoms, not 12 N_A.

⚠️

Student Fallacy (Why candidates pick this trap): Forgetting to multiply NaOH by atomicity 3 or miscalculating 240/40.

2 B

✓ 100% Correct

Verdict & Scientific Reason:

100% correct. A, B, and D each contain exactly 12 moles of atoms (12 N_A).

💡

Why this is airtight: None; precise stoichiometric evaluation.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Includes C (18 N_A).

⚠️

Student Fallacy (Why candidates pick this trap): Including C instead of A.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. E has 15 N_A atoms.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming CO₂ has 12 N_A atoms.

⚠️

NTA Trap Alert: Counting Moles of Molecules Instead of Moles of Atoms

Candidates sometimes only compute moles of the molecule (A = 2, B = 4, C = 6, D = 6, E = 5) and erroneously conclude that C and D are equal! The question explicitly asks for the NUMBER OF ATOMS, requiring multiplication by atomicity!

🛡️ How to avoid the -1 mark: Always underline "NUMBER OF ATOMS" and multiply by the formula unit atom count!

📖

Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · Some Basic Concepts of Chemistry Standard Benchmark

Core Scientific Principle Tested:

"Number of atoms = (mass / molar mass) × atomicity × N_A."

Syllabus Focus: Mole Concept and Atomic Stoichiometry

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Multiply by atoms in formula: A=12, B=12, D=12 ⟹ A, B, and D only!

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NEET 2025 Chemistry Question 68 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Moles × Atomicity Calculation Shortcut

Step-by-Step Rigorous Workflow & Mathematical Proof

Formulate Equation for Total Number of Atoms

Calculate Atoms for Substances A, B, and C

Calculate Atoms for Substances D and E and Match

360° Option Elimination Engine Key Feature

NTA Trap Alert: Counting Moles of Molecules Instead of Moles of Atoms

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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