NEET 2017 Previous Year Question Paper

1. A uniform wire of resistance R is stretched to twice its original length, its volume remaining constant. Its new resistance is

   1. 4R
   2. R/2
   3. 2R
   4. R/4
   Answer and explanation

   Answer: A (4R)

   R = ρl/A and volume lA is constant, so A halves when l doubles. R′ = ρ(2l)/(A/2) = 4R.

2. A planet has 8 times the mass and 2 times the radius of the Earth. If the escape velocity on Earth is 11.2 km/s, on the planet it is

   1. 11.2 km/s
   2. 22.4 km/s
   3. 5.6 km/s
   4. 44.8 km/s
   Answer and explanation

   Answer: B (22.4 km/s)

   vₑ = √(2GM/R) ∝ √(M/R) = √(8/2) = 2. So vₑ = 2 × 11.2 = 22.4 km/s.

3. The de Broglie wavelength of an electron accelerated from rest through a potential difference of 100 V is about

   1. 1.23 nm
   2. 0.0123 nm
   3. 0.123 nm
   4. 12.3 nm
   Answer and explanation

   Answer: C (0.123 nm)

   λ = h/√(2meV) = 6.626 × 10⁻³⁴ / √(2 × 9.11 × 10⁻³¹ × 1.6 × 10⁻¹⁹ × 100) ≈ 1.23 × 10⁻¹⁰ m = 0.123 nm (equivalently 12.27/√V Å).

4. An object is placed 30 cm in front of a convex lens of focal length 20 cm. The image is

   1. virtual, 60 cm in front of the lens, magnification +2
   2. real, 60 cm behind the lens, magnification −2
   3. real, 12 cm behind the lens, magnification −0.4
   4. real, 60 cm behind the lens, magnification −0.5
   Answer and explanation

   Answer: B (real, 60 cm behind the lens, magnification −2)

   1/v − 1/u = 1/f with u = −30, f = +20: 1/v = 1/20 − 1/30 = 1/60, so v = +60 cm (real). m = v/u = 60/(−30) = −2 (inverted, twice the size).

5. A radioactive isotope has a half-life of 5 days. The fraction of a sample remaining after 15 days is

   1. 1/6
   2. 1/16
   3. 1/3
   4. 1/8
   Answer and explanation

   Answer: D (1/8)

   15 days = 3 half-lives, so N/N₀ = (1/2)³ = 1/8.

6. A pipe closed at one end is 33 cm long. If the speed of sound is 330 m/s, its fundamental frequency is (ignore end correction)

   1. 500 Hz
   2. 250 Hz
   3. 1000 Hz
   4. 125 Hz
   Answer and explanation

   Answer: B (250 Hz)

   Closed pipe fundamental: f = v/4L = 330/(4 × 0.33) = 250 Hz.

7. The bond order of the superoxide ion O₂⁻ is

   1. 2.5
   2. 1
   3. 1.5
   4. 2
   Answer and explanation

   Answer: C (1.5)

   O₂ has bond order (10 − 6)/2 = 2. Adding one electron to an antibonding π* orbital gives (10 − 7)/2 = 1.5.

8. 9.8 g of H₂SO₄ (molar mass 98 g/mol) is dissolved in 500 g of water. The molality of the solution is

   1. 0.2 m
   2. 0.02 m
   3. 0.1 m
   4. 0.5 m
   Answer and explanation

   Answer: A (0.2 m)

   Moles = 9.8/98 = 0.1 mol. Molality = 0.1 mol / 0.5 kg = 0.2 mol/kg.

9. Which of the following alkenes shows geometrical (cis–trans) isomerism?

   1. But-2-ene
   2. Propene
   3. 2-Methylpropene
   4. But-1-ene
   Answer and explanation

   Answer: A (But-2-ene)

   Each doubly bonded carbon must carry two different groups. In but-2-ene, CH₃CH=CHCH₃, each carbon has H and CH₃, so cis and trans forms exist; the others have two identical groups on one carbon.

10. Zirconium and hafnium have almost identical atomic radii. This is mainly due to

    1. diagonal relationship
    2. inert pair effect
    3. lanthanoid contraction
    4. actinoid contraction
    Answer and explanation

    Answer: C (lanthanoid contraction)

    The poorly shielding 4f electrons filled between La and Hf cause the lanthanoid contraction, which cancels the expected size increase from period 5 to period 6.

11. For N₂(g) + 3H₂(g) → 2NH₃(g) at 300 K, the value of ΔH − ΔU is about (R = 8.314 J mol⁻¹ K⁻¹)

    1. −4.99 kJ
    2. −2.49 kJ
    3. +4.99 kJ
    4. zero
    Answer and explanation

    Answer: A (−4.99 kJ)

    ΔH − ΔU = Δn(g)RT. Δn(g) = 2 − 4 = −2, so ΔH − ΔU = −2 × 8.314 × 300 J ≈ −4988 J ≈ −4.99 kJ.

12. Which of the following gives a silver mirror with Tollens' reagent?

    1. Propanone
    2. Ethanol
    3. Ethanal
    4. Ethanoic acid
    Answer and explanation

    Answer: C (Ethanal)

    Tollens' reagent oxidises aldehydes; ethanal (CH₃CHO) reduces Ag⁺ to metallic silver. Ketones, alcohols and carboxylic acids (except formic acid) do not.

Botany

13. Casparian strips are found in the

    1. epidermis
    2. pericycle
    3. cortex
    4. endodermis
    Answer and explanation

    Answer: D (endodermis)

    The radial and inner tangential walls of endodermal cells carry suberin bands (Casparian strips) that block apoplastic water movement into the stele.

14. How many meiotic divisions are needed to produce 100 seeds in an angiosperm?

    1. 100
    2. 200
    3. 125
    4. 150
    Answer and explanation

    Answer: C (125)

    Each seed needs one egg (1 megaspore mother cell meiosis gives 1 functional megaspore) and one pollen grain (1 meiosis gives 4 pollen grains). 100 seeds: 100 + 100/4 = 125 meioses.

15. Okazaki fragments are formed during DNA replication on the

    1. template strand only, during transcription
    2. leading strand, synthesised continuously
    3. RNA primer itself
    4. lagging strand, synthesised discontinuously
    Answer and explanation

    Answer: D (lagging strand, synthesised discontinuously)

    DNA polymerase works only 5′→3′, so the strand whose template runs 5′→3′ towards the fork is made in short pieces (Okazaki fragments) later joined by DNA ligase.

16. Which plant hormone causes stomatal closure during water stress?

    1. Abscisic acid
    2. Gibberellin
    3. Cytokinin
    4. Auxin
    Answer and explanation

    Answer: A (Abscisic acid)

    ABA, the stress hormone, accumulates in guard cells under water stress and causes stomata to close.

17. Which of the following is NOT a greenhouse gas?

    1. Nitrous oxide
    2. Nitrogen
    3. Carbon dioxide
    4. Methane
    Answer and explanation

    Answer: B (Nitrogen)

    N₂ does not absorb infrared radiation; CO₂, CH₄, N₂O and CFCs are greenhouse gases.

18. In a test cross of a heterozygous tall pea plant (Tt), the expected ratio of tall to dwarf offspring is

    1. 1 : 2 : 1
    2. 1 : 1
    3. 3 : 1
    4. All tall
    Answer and explanation

    Answer: B (1 : 1)

    Tt × tt gives Tt and tt in equal numbers: 1 tall : 1 dwarf.

Zoology

19. If the stroke volume of a person is 70 mL and the heart rate is 72 beats per minute, the cardiac output is about

    1. 0.5 L/min
    2. 5 L/min
    3. 50 L/min
    4. 7.2 L/min
    Answer and explanation

    Answer: B (5 L/min)

    Cardiac output = stroke volume × heart rate = 70 mL × 72 = 5040 mL/min ≈ 5 L/min.

20. Which of the following hormones is derived from the amino acid tyrosine?

    1. Thyroxine
    2. Insulin
    3. Progesterone
    4. Cortisol
    Answer and explanation

    Answer: A (Thyroxine)

    Thyroxine (and adrenaline) are iodothyronine/catecholamine derivatives of tyrosine; cortisol and progesterone are steroids; insulin is a peptide.

21. In humans, fertilisation normally occurs in the

    1. isthmus of the fallopian tube
    2. ampullary region of the fallopian tube
    3. uterus
    4. cervix
    Answer and explanation

    Answer: B (ampullary region of the fallopian tube)

    The ovum is fertilised in the ampullary region (ampullary–isthmic junction) of the oviduct, after which the zygote moves towards the uterus.

22. The wings of a butterfly and the wings of a bird are an example of

    1. vestigial organs
    2. analogous organs and convergent evolution
    3. homologous organs and divergent evolution
    4. atavism
    Answer and explanation

    Answer: B (analogous organs and convergent evolution)

    They do the same job but have different structure and origin (analogous), produced by convergent evolution.

23. The Widal test is used to diagnose

    1. tuberculosis
    2. malaria
    3. typhoid
    4. pneumonia
    Answer and explanation

    Answer: C (typhoid)

    Typhoid fever (Salmonella typhi) is confirmed by the Widal test.

24. Which part of the nephron is almost impermeable to water?

    1. Proximal convoluted tubule
    2. Ascending limb of the loop of Henle
    3. Descending limb of the loop of Henle
    4. Collecting duct under ADH
    Answer and explanation

    Answer: B (Ascending limb of the loop of Henle)

    The ascending limb transports electrolytes out but is nearly impermeable to water, helping build the medullary osmotic gradient.