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NEET UG previous-year-style questions — NCERT-anchored Biology, application-heavy Physics (electrodynamics, modern physics) and the trickier Chemistry (thermodynamics, coordination compounds) that separate top rankers.

20 questionsStep-by-step solutionsPhysics · Chemistry · Biology
PhysicsPhysical ChemistryInorganic ChemistryOrganic ChemistryBotanyZoology
  1. 1Physics · Current ElectricityHardNumerical

    Three resistors of 6 Ω6\ \Omega each are connected in parallel. What is the equivalent resistance (in Ω\Omega)?

    Show answer & solution
    Correct answer
    2
    Solution

    1R=16+16+16=36=12⇒R=2 Ω\dfrac{1}{R} = \dfrac{1}{6}+\dfrac{1}{6}+\dfrac{1}{6} = \dfrac{3}{6} = \dfrac{1}{2} \Rightarrow R = 2\ \Omega.

  2. 2Physics · Modern PhysicsHardNumerical

    The half-life of a radioactive sample is 1010 years. What fraction of the original nuclei remains after 3030 years?

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    Correct answer
    1/81/8
    Solution

    3030 years =3= 3 half-lives. Remaining fraction =(1/2)3=1/8= (1/2)^3 = 1/8.

  3. 3Physics · ElectrodynamicsHardMCQ

    A charged particle moves parallel to a uniform magnetic field. The magnetic force on it is:

    • A) Maximum
    • B) Zero
    • C) Perpendicular to velocity
    • D) Along the field
    Show answer & solution
    Correct answer
    B
    Solution

    F⃗=qv⃗×B⃗\vec F = q\vec v \times \vec B. When v⃗∥B⃗\vec v \parallel \vec B, the angle is 0∘0^{\circ}, so sin⁡θ=0\sin\theta = 0 and the force is zero.

  4. 4Physics · Ray OpticsMediumNumerical

    The refractive index of a medium is 1.51.5. What is the critical angle for total internal reflection at the medium–air interface? (give sin⁡\sin of the angle)

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    Correct answer
    sin C=2/3C = 2/3 ≈ 0.667 (C ≈ 41.8°)
    Solution

    sin⁡C=1n=11.5=23≈0.667\sin C = \dfrac{1}{n} = \dfrac{1}{1.5} = \dfrac{2}{3} \approx 0.667, giving C≈41.8∘C \approx 41.8^{\circ}.

  5. 5Chemistry · ThermodynamicsHardMCQ

    For which process is entropy change (ΔS\Delta S) NEGATIVE?

    • A) Melting of ice
    • B) Vaporization of water
    • C) 2H2(g)+O2(g)→2H2O(l)\mathrm{2H_2(g) + O_2(g) \to 2H_2O(l)}
    • D) Dissolution of salt in water
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    Correct answer
    C
    Solution

    Three moles of gas form two moles of liquid — a large decrease in disorder, so ΔS<0\Delta S < 0. The other options all increase molecular freedom/disorder.

  6. 6Chemistry · Coordination CompoundsHardNumerical

    Calculate the spin-only magnetic moment (in BM) of [Co(NH3)6]3+[\mathrm{Co(NH_3)_6}]^{3+} (a low-spin complex).

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    Correct answer
    0
    Solution

    Co3+\mathrm{Co}^{3+} is d6d^6. NH3\mathrm{NH_3} is a strong-field ligand → low-spin, pairing all 66 electrons in t2gt_{2g}. With n=0n=0 unpaired electrons, μ=0\mu = 0 BM (diamagnetic).

  7. 7Chemistry · EquilibriumMediumNumerical

    The pH\mathrm{pH} of a solution is 44. What is the hydroxide ion concentration [OH−][\mathrm{OH^-}] (in mol/L)?

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    Correct answer
    1e−101e-10
    Solution

    [H+]=10−4[\mathrm{H^+}] = 10^{-4}. Since [H+][OH−]=10−14[\mathrm{H^+}][\mathrm{OH^-}] = 10^{-14}, [OH−]=10−14/10−4=10−10 mol/L[\mathrm{OH^-}] = 10^{-14}/10^{-4} = 10^{-10}\ \text{mol/L}.

  8. 8Chemistry · d & f BlockHardMCQ

    Which of the following has the maximum number of unpaired electrons?

    • A) Mn2+\mathrm{Mn}^{2+}
    • B) Fe2+\mathrm{Fe}^{2+}
    • C) Co2+\mathrm{Co}^{2+}
    • D) Ni2+\mathrm{Ni}^{2+}
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    Correct answer
    A
    Solution

    Mn2+\mathrm{Mn}^{2+} is d5d^5 (5 unpaired), Fe2+\mathrm{Fe}^{2+} d6d^6 (4), Co2+\mathrm{Co}^{2+} d7d^7 (3), Ni2+\mathrm{Ni}^{2+} d8d^8 (2). Maximum is Mn2+\mathrm{Mn}^{2+}.

  9. 9Chemistry · OrganicMediumMCQ

    Which effect explains the greater acidity of chloroacetic acid compared to acetic acid?

    • A) +I effect of Cl
    • B) −I (inductive electron−withdrawingelectron-withdrawing) effect of Cl
    • C) Resonance donation by Cl
    • D) Hyperconjugation
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    Correct answer
    B
    Solution

    Chlorine’s electron-withdrawing −I-I effect stabilizes the carboxylate anion by dispersing its negative charge, making the O–H more acidic (pKapK_a of chloroacetic acid ≈2.9\approx 2.9 vs 4.764.76 for acetic acid).

  10. 10Botany · Molecular Basis of InheritanceHardMCQ

    In the lac operon of E. coli, the role of the repressor protein binding to the operator is to:

    • A) Increase transcription of structural genes
    • B) Bind lactose directly
    • C) Block RNA polymerase from transcribing the structural genes
    • D) Code for β-galactosidase
    Show answer & solution
    Correct answer
    C
    Solution

    The repressor (product of the i gene) binds the operator and physically blocks RNA polymerase, switching the operon OFF. When lactose (inducer) binds the repressor, it detaches and transcription proceeds.

  11. 11Botany · Plant PhysiologyMediumMCQ

    In C4 plants, the primary CO₂ acceptor and the first stable product are:

    • A) RuBP and 3−PGA3-PGA
    • B) PEP and oxaloacetate (OAA)
    • C) PEP and 3−PGA3-PGA
    • D) RuBP and OAA
    Show answer & solution
    Correct answer
    B
    Solution

    In C4 plants the mesophyll enzyme PEP carboxylase fixes CO₂ onto phosphoenolpyruvate (PEP), giving the 4−carbon4-carbon oxaloacetate — hence "C4". (RuBP+3−PGARuBP + 3-PGA is the C3 pathway.)

  12. 12Zoology · Human ReproductionMediumMCQ

    Which hormone surge directly triggers ovulation in the human menstrual cycle?

    • A) FSH
    • B) Progesterone
    • C) LH
    • D) Estrogen
    Show answer & solution
    Correct answer
    C
    Solution

    A sharp mid−cyclemid-cycle surge of Luteinizing Hormone (LH) around day 14 triggers rupture of the Graafian follicle and release of the secondary oocyte (ovulation).

  13. 13Zoology · BiotechnologyHardMCQ

    In recombinant DNA technology, the enzyme used to join DNA fragments (seal the phosphodiester backbone) is:

    • A) Restriction endonuclease
    • B) DNA polymerase
    • C) DNA ligase
    • D) Helicase
    Show answer & solution
    Correct answer
    C
    Solution

    Restriction enzymes cut DNA at specific sites; DNA ligase then seals the sticky/bluntsticky/blunt ends by forming phosphodiester bonds, creating the recombinant molecule.

  14. 14Zoology · Animal KingdomMediumMCQ

    Which feature is characteristic of Phylum Echinodermata?

    • A) Bilateral symmetry throughout life
    • B) Water vascular system
    • C) Open circulatory system with haemocyanin
    • D) Presence of nematocysts
    Show answer & solution
    Correct answer
    B
    Solution

    Echinoderms (starfish, sea urchins) possess a unique water vascular system used for locomotion, feeding and respiration. They are radially symmetric as adults (bilateral only as larvae).

  15. 15Botany · GeneticsHardNumerical

    In a dihybrid cross (RrYy×RrYy\mathrm{RrYy} \times \mathrm{RrYy}) following independent assortment, what fraction of the offspring are homozygous recessive for both traits (rryy\mathrm{rryy})?

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    Correct answer
    1/161/16
    Solution

    Each recessive homozygote occurs with probability 1/41/4; independent assortment multiplies them: 1/4×1/4=1/161/4 \times 1/4 = 1/16.

  16. 16Physics · SemiconductorsMediumMCQ

    In an n−typen-type semiconductor, the majority charge carriers are:

    • A) Holes
    • B) Electrons
    • C) Protons
    • D) Positive ions
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    Correct answer
    B
    Solution

    n−typen-type material is doped with pentavalent atoms (e.g., P, As) contributing free electrons, which become the majority carriers; holes are the minority carriers.

  17. 17Chemistry · PhysicalHardNumerical

    A first-order reaction has a rate constant k=0.693 min−1k = 0.693\ \text{min}^{-1}. What is its half-life (in minutes)?

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    Correct answer
    1
    Solution

    For a first-order reaction t1/2=0.693k=0.6930.693=1t_{1/2} = \dfrac{0.693}{k} = \dfrac{0.693}{0.693} = 1 min.

  18. 18Physics · MechanicsMediumNumerical

    A body of mass 22 kg moving at 33 m/s collides and sticks to a 11 kg body at rest. Find the common velocity after collision (in m/s).

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    Correct answer
    2
    Solution

    Conservation of momentum: 2×3+1×0=(2+1)v⇒6=3v⇒v=22 \times 3 + 1 \times 0 = (2+1)v \Rightarrow 6 = 3v \Rightarrow v = 2 m/s.

  19. 19Botany · Cell BiologyMediumMCQ

    The site of the light−independentlight-independent reactions (Calvin cycle) of photosynthesis is the:

    • A) Thylakoid membrane
    • B) Stroma of the chloroplast
    • C) Mitochondrial matrix
    • D) Grana
    Show answer & solution
    Correct answer
    B
    Solution

    The Calvin cycle (carbon fixation) occurs in the stroma, using ATP and NADPH generated by the light reactions on the thylakoid membranes.

  20. 20Zoology · Human PhysiologyHardMCQ

    Oxygen is transported in blood mainly as:

    • A) Dissolved in plasma
    • B) Bicarbonate ions
    • C) Oxyhaemoglobin
    • D) Carbaminohaemoglobin
    Show answer & solution
    Correct answer
    C
    Solution

    About 97%97\% of oxygen is carried bound to haemoglobin as oxyhaemoglobin; only ∼3%\sim3\% is dissolved in plasma. (Bicarbonate and carbamino forms are how CO₂ is transported.)

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