Q.117 Chemistry ⭐ 360° Option Elimination Active

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NEET 2020 Chemistry Question 117 Solution

Topic: Biomolecules · Official NTA Booklet Code E1

Question

Which of the following is a basic amino acid?

(1)Serine
(2)Alanine
(3)Tyrosine
(4)Lysine

✓

Verified Against NTA Final Answer Key

Option (4) : Lysine

📚 Biomolecules Easy

📋 Given Parameters & Problem Setup

Category Basic amino acid (contains extra -NH2 in side chain)

Candidate Amino Acids Serine, Alanine, Tyrosine, Lysine

⚡

The 30-Second Exam Hall Shortcut: ⚡ "Basic Amino Acids = L-A-H (Lysine, Arginine, Histidine)!"

⏱️ 15 seconds

Basic amino acids contain more amino groups than carboxyl groups. The canonical basic amino acids highlighted in NCERT are Lysine, Arginine, and Histidine. Serine has a neutral -CH2OH; Alanine has neutral -CH3; Tyrosine is aromatic. Mark Lysine (Option 4) in 5 seconds!

1 Serine: -CH2OH (neutral, polar).

2 Alanine: -CH3 (neutral, non-polar).

3 Tyrosine: -CH2-C6H4-OH (aromatic, neutral).

4 Lysine: -(CH2)4-NH2 (basic, cationic at physiological pH).

5 Select Option (4) Lysine.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Chemistry · Biomolecules (Amino Acids: Classification into Acidic, Basic and Neutral)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Classification Criteria of Amino Acids

Amino acids contain amino ( $-\text{NH}_2$ ) and carboxyl ( $-\text{COOH}$ ) functional groups. Depending on the relative number of amino and carboxyl groups in the whole molecule (including side chain $R$ ), amino acids are classified as acidic, basic, or neutral.

Step 2

Define Basic Amino Acids

An amino acid is basic when it contains more basic amino groups than acidic carboxyl groups. In Lysine, the side chain is $-(\text{CH}_2)_4-\text{NH}_2$ , containing a terminal $\varepsilon$ -amino group which accepts a proton at physiological pH ( $\text{pK}_a \approx 10.5$ ), giving it a net positive charge.

Step 3

Evaluate Other Candidate Amino Acids

- Alanine ( $R = -\text{CH}_3$ ): Equal number of amino and carboxyl groups -> Neutral amino acid. - Serine ( $R = -\text{CH}_2\text{OH}$ ): Contains neutral alcoholic group -> Neutral polar amino acid. - Tyrosine ( $R = -\text{CH}_2-\text{C}_6\text{H}_4-\text{OH}$ ): Phenolic group -> Aromatic amino acid.

Step 4

Conclude Lysine

Lysine is the only basic amino acid present among the options.

⭐

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; serine is a neutral amino acid containing a polar hydroxymethyl side chain.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing polar neutral side chains with basic side chains.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; alanine is an aliphatic neutral amino acid with a methyl side chain.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking aliphatic amino acids are basic.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; tyrosine is an aromatic amino acid, slightly weakly acidic due to phenolic OH, not basic.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing aromatic amino acids with basic amino acids.

4 D

✓ 100% Correct

Verdict & Scientific Reason:

Factually exact; lysine possesses two amino groups and one carboxyl group, making it a basic amino acid.

💡

Why this is airtight: None; fundamental biomolecule classification.

⚠️

NTA Trap Alert: Repetition in NEET 2020

NEET 2020 tested basic amino acids in BOTH Zoology (Q79) and Chemistry (Q117)! In both questions, Lysine was the correct answer.

🛡️ How to avoid the -1 mark: Remember: Basic amino acids = Lysine and Arginine!

📖

Core NEET Syllabus Standard

Chemistry · Biomolecules Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Classification of Amino Acids: Lysine as a Basic Amino Acid

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Chemistry Question 117 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Basic Amino Acids = L-A-H (Lysine, Arginine, Histidine)!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Classification Criteria of Amino Acids

Define Basic Amino Acids

Evaluate Other Candidate Amino Acids

Conclude Lysine

360° Option Elimination Engine Key Feature

NTA Trap Alert: Repetition in NEET 2020

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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