Q.191 Zoology ⭐ 360° Option Elimination Active

NEET 2021 Zoology Question 191 Solution

Topic: Biomolecules · Official NTA Booklet Code M1

Question

Following are the statements with reference to 'lipids'. (a) Lipids having only single bonds are called unsaturated fatty acids. (b) Lecithin is a phospholipid. (c) Trihydroxy propane is glycerol. (d) Palmitic acid has 20 carbon atoms including carboxyl carbon. (e) Arachidonic acid has 16 carbon atoms. Choose the correct answer from the options given below.

(1)(a) and (b) only
(2)(c) and (d) only
(3)(b) and (c) only
(4)(b) and (e) only

✓

Verified Against NTA Final Answer Key

Option (3) : (b) and (c) only

📚 Biomolecules Medium

📋 Given Parameters & Problem Setup

Statement (a) Lipids having only single bonds are called unsaturated fatty acids

Statement (b) Lecithin is a phospholipid

Statement (c) Trihydroxy propane is glycerol

Statement (d) Palmitic acid has 20 carbon atoms including carboxyl carbon

Statement (e) Arachidonic acid has 16 carbon atoms

⚡

The 30-Second Exam Hall Shortcut: ⚡ "NTA Carbon Swap Trap: Palmitic has 16 Carbons, Arachidonic has 20 Carbons!"

⏱️ Save ~30 seconds

Palmitic acid has 16 carbons (not 20, eliminates (d)) and Arachidonic acid has 20 carbons (not 16, eliminates (e)). Fatty acids with only single bonds are SATURATED (not unsaturated, eliminates (a)). Lecithin is indeed a phospholipid (b is True) and Trihydroxypropane is glycerol (c is True). Only (b) and (c) survive! Option (3) is correct.

1 Check carbon counts: Palmitic acid = 16 carbons; Arachidonic acid = 20 carbons. Statements (d) and (e) are swapped by NTA and are both FALSE!

2 Check bond classification: Only single bonds = Saturated fatty acid. Statement (a) calls them unsaturated -> FALSE!

3 Check surviving statements: (b) Lecithin is a phospholipid (True), (c) Glycerol is trihydroxy propane (True).

4 Select Option (3): (b) and (c) only.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Biomolecules (Lipids: Fatty acids could be saturated (without double bond) or unsaturated (with one or more C=C double bonds). Palmitic acid has 16 carbons including carboxyl carbon. Arachidonic acid has 20 carbon atoms including the carboxyl carbon. Glycerol is trihydroxy propane. Lecithin is a phospholipid found in cell membrane).

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Chemical Dissection of Each Lipid Statement

- Statement (a) (FALSE): Fatty acids possessing only single carbon-carbon bonds ( $-\text{C}-\text{C}-$ ) along their aliphatic acyl chain are termed saturated fatty acids (e.g. palmitic, stearic). Fatty acids possessing one or more double bonds ( $-\text{C}=\text{C}-$ ) are termed unsaturated fatty acids (e.g. oleic, linoleic, arachidonic). - Statement (b) (TRUE): Lecithin (phosphatidylcholine) is a major membrane phospholipid composed of glycerol esterified to two fatty acids, a phosphate group, and a choline nitrogenous head group. - Statement (c) (TRUE): Glycerol is chemically designated as trihydroxy propane, with the IUPAC structural formula $\text{CH}_2\text{OH}-\text{CHOH}-\text{CH}_2\text{OH}$ (propane-1,2,3-triol). - Statement (d) (FALSE): Palmitic acid is a 16-carbon saturated fatty acid ( $ext{CH}_3(\text{CH}_2)_{14}\text{COOH}$ ), possessing 16 carbon atoms including the carboxyl carbon, NOT 20. - Statement (e) (FALSE): Arachidonic acid is a polyunsaturated fatty acid with 4 double bonds that contains 20 carbon atoms including the carboxyl carbon, NOT 16.

\begin{aligned} \text{Palmitic Acid} &\implies \mathbf{16\text{ Carbons}} \quad [\text{Statement (d) is False}] \\ \text{Arachidonic Acid} &\implies \mathbf{20\text{ Carbons}} \quad [\text{Statement (e) is False}] \\ \text{Single bonds only} &\implies \mathbf{Saturated} \quad [\text{Statement (a) is False}] \\ \text{Glycerol} &\iff \text{Trihydroxy propane} \quad [\text{Statement (c) is True}] \\ \text{Lecithin} &\iff \text{Phospholipid} \quad [\text{Statement (b) is True}] \end{aligned}

Step 2

Synthesis of Valid Choices

Only statements (b) and (c) are true statements. This leads exclusively to Option (3).

⭐

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 1

✗ Incorrect

Verdict & Scientific Reason:

Incorrect because statement (a) is false (single bonds characterize saturated lipids).

⚠️

Student Fallacy (Why candidates pick this trap): Confusing saturated with unsaturated fatty acids.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Incorrect because statement (d) is false (palmitic acid has 16 carbons, not 20).

⚠️

Student Fallacy (Why candidates pick this trap): Failing to remember the carbon number of palmitic acid.

3 3

✓ 100% Correct

Verdict & Scientific Reason:

Correct. Accurately identifies Lecithin as a phospholipid and Glycerol as trihydroxy propane.

💡

Why this is airtight: None. Candidate identifies the NTA carbon number swap in (d) and (e).

4 4

✗ Incorrect

Verdict & Scientific Reason:

Incorrect because statement (e) is false (arachidonic acid has 20 carbons, not 16).

⚠️

Student Fallacy (Why candidates pick this trap): Accepting the swapped carbon count for arachidonic acid.

⚠️

NTA Trap Alert: The Palmitic (16) vs Arachidonic (20) Mirror Inversion Trap

NTA paper setters frequently take two numbers from the same textbook paragraph and cross-swap them: they assign 20 carbons to Palmitic acid and 16 carbons to Arachidonic acid. Always double-check which fatty acid has 16 vs 20 carbons.

🛡️ How to avoid the -1 mark: Use the mnemonic: "P comes before A alphabetically, and 16 comes before 20 numerically" -> Palmitic = 16, Arachidonic = 20.

📖

Core NEET Syllabus Standard

NEET / NCERT Biology · Biomolecules Standard Benchmark

Core Scientific Principle Tested:

"Lecithin is a phospholipid; glycerol is trihydroxy propane; palmitic acid has 16 carbons; arachidonic acid has 20 carbons."

Syllabus Focus: Structure and Types of Lipids

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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Classification & Functions of Biomolecules (Proteins, Polysaccharides & Secondary Metabolites)

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NEET 2021 Zoology Question 191 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "NTA Carbon Swap Trap: Palmitic has 16 Carbons, Arachidonic has 20 Carbons!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Chemical Dissection of Each Lipid Statement

Synthesis of Valid Choices

360° Option Elimination Engine Key Feature

NTA Trap Alert: The Palmitic (16) vs Arachidonic (20) Mirror Inversion Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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