NEST Practice Set 1

NEST · 2026 · with answers and explanations

questions
30
Total marks
90
Duration
200 minutes
Negative marking
−1

Subjects: Biology · Chemistry · Mathematics · Physics · Aptitude (Reasoning)

Question 1

Biology · 3 marks · −1

The cell membrane is primarily composed of:

  1. A.Proteins and nucleic acids
  2. B.Phospholipids and proteins
  3. C.Carbohydrates and lipids
  4. D.Cellulose and starch

Correct answer: B

Explanation: The cell membrane follows the fluid mosaic model, consisting primarily of a phospholipid bilayer with embedded and peripheral proteins. Cholesterol and glycolipids are also present in animal cells.

Question 2

Biology · 3 marks · −1

Enzymes increase the rate of a chemical reaction by:

  1. A.Increasing the temperature of the system
  2. B.Lowering the activation energy
  3. C.Increasing the concentration of reactants
  4. D.Changing the equilibrium constant

Correct answer: B

Explanation: Enzymes act as biological catalysts by lowering the activation energy of a reaction, providing an alternative pathway with a lower energy barrier. They do not alter the equilibrium position or the overall free energy change.

Question 3

Biology · 3 marks · −1

In a dihybrid cross between two heterozygous parents (AaBb × AaBb), the fraction of offspring homozygous for both traits (AABB or aabb) is:

  1. A.1/4
  2. B.1/8
  3. C.1/16
  4. D.3/16

Correct answer: B

Explanation: P(AABB) = (1/4)(1/4) = 1/16. P(aabb) = (1/4)(1/4) = 1/16. Total probability = 1/16 + 1/16 = 2/16 = 1/8.

Question 4

Biology · 3 marks · −1

During DNA replication, the enzyme that removes RNA primers and replaces them with DNA nucleotides is:

  1. A.DNA polymerase III
  2. B.DNA polymerase I
  3. C.Primase
  4. D.Helicase

Correct answer: B

Explanation: In prokaryotes, DNA polymerase I uses its 5'→3' exonuclease activity to remove RNA primers and its polymerase activity to fill the resulting gaps with DNA nucleotides. DNA ligase then seals the remaining nicks.

Question 5

Biology · 3 marks · −1

The C₄ pathway of carbon fixation differs from C₃ in that:

  1. A.CO₂ is first fixed into a 4-carbon compound by PEP carboxylase
  2. B.It occurs only at night
  3. C.It does not require the Calvin cycle
  4. D.Rubisco is absent in C₄ plants

Correct answer: A

Explanation: In C₄ plants, CO₂ is initially fixed by PEP carboxylase in mesophyll cells into oxaloacetate (a 4-carbon compound). The CO₂ is then released in bundle sheath cells where the Calvin cycle operates. C₄ plants still use Rubisco.

Question 6

Biology · 3 marks · −1

Oxygenated blood from the lungs first arrives in which chamber of the human heart?

  1. A.Right atrium
  2. B.Left atrium
  3. C.Right ventricle
  4. D.Left ventricle

Correct answer: B

Explanation: Oxygenated blood from the lungs returns via the pulmonary veins to the left atrium. From there, it passes to the left ventricle, which pumps it to the body through the aorta.

Question 7

Biology · 3 marks · −1

In an ecological pyramid of energy:

  1. A.It can be inverted
  2. B.It is always upright
  3. C.It depends on the ecosystem type
  4. D.Producers occupy the top level

Correct answer: B

Explanation: The pyramid of energy is always upright because energy transfer between trophic levels follows the second law of thermodynamics. Only about 10% of energy is transferred from one level to the next.

Question 8

Chemistry · 3 marks · −1

How many lone pairs of electrons are present on the oxygen atom in water (H₂O)?

  1. A.0
  2. B.1
  3. C.2
  4. D.3

Correct answer: C

Explanation: Oxygen in H₂O has 6 valence electrons. Two electrons are shared in bonds with hydrogen, and four remain as two lone pairs. This gives water its bent shape with a bond angle of about 104.5°.

Question 9

Chemistry · 3 marks · −1

For an ideal gas undergoing an isothermal expansion, the change in internal energy (ΔU) is:

  1. A.Positive
  2. B.Zero
  3. C.Negative
  4. D.Equal to the work done on the gas

Correct answer: B

Explanation: For an ideal gas, internal energy depends only on temperature: U = f(T). In an isothermal process (constant T), ΔU = 0. The work done by the gas equals the heat absorbed: W = Q = nRT ln(V₂/V₁).

Question 10

Chemistry · 3 marks · −1

Which of the following is a colligative property?

  1. A.Viscosity
  2. B.Surface tension
  3. C.Elevation of boiling point
  4. D.Optical rotation

Correct answer: C

Explanation: Colligative properties depend only on the number of solute particles, not their chemical identity. Elevation of boiling point, depression of freezing point, vapor pressure lowering, and osmotic pressure are all colligative properties.

Question 11

Chemistry · 3 marks · −1

Which element has the highest electronegativity on the Pauling scale?

  1. A.Sodium
  2. B.Chlorine
  3. C.Fluorine
  4. D.Oxygen

Correct answer: C

Explanation: Fluorine has the highest electronegativity (3.98 on the Pauling scale) of all elements. Electronegativity generally increases across a period and up a group in the periodic table.

Question 12

Chemistry · 3 marks · −1

Markovnikov's rule states that during the addition of HX to an unsymmetrical alkene, the hydrogen atom adds to:

  1. A.The carbon with fewer hydrogen atoms
  2. B.The carbon with more hydrogen atoms
  3. C.Either carbon equally
  4. D.The carbon adjacent to an electron-withdrawing group

Correct answer: B

Explanation: Markovnikov's rule states that in the ionic addition of HX to an unsymmetrical alkene, the hydrogen adds to the carbon with more hydrogen atoms (less substituted), and the halide adds to the more substituted carbon, forming the more stable carbocation intermediate.

Question 13

Chemistry · 4 marks · −1

The IUPAC name of CH₃COCH₃ is:

  1. A.Propanal
  2. B.Propan-2-one
  3. C.Propan-1-ol
  4. D.Propanoic acid

Correct answer: B

Explanation: CH₃COCH₃ is acetone, whose IUPAC name is propan-2-one. It is the simplest ketone with three carbon atoms, and the carbonyl group is on the second carbon. The suffix '-one' indicates a ketone functional group.

Question 14

Chemistry · 3 marks · −1

For a second-order reaction 2A → Products, the half-life is:

  1. A.Independent of initial concentration
  2. B.Inversely proportional to initial concentration
  3. C.Directly proportional to initial concentration
  4. D.Proportional to the square of initial concentration

Correct answer: B

Explanation: For a second-order reaction with rate = k[A]², the half-life is t₁/₂ = 1/(k[A]₀), which is inversely proportional to the initial concentration. Doubling the initial concentration halves the half-life.

Question 15

Mathematics · 3 marks · −1

The modulus of the complex number 3 + 4i is:

  1. A.7
  2. B.5
  3. C.25
  4. D.1

Correct answer: B

Explanation: The modulus of z = a + bi is |z| = √(a² + b²) = √(9 + 16) = √25 = 5.

Question 16

Mathematics · 3 marks · −1

The number of ways to choose a committee of 3 from 8 people is:

  1. A.24
  2. B.56
  3. C.336
  4. D.512

Correct answer: B

Explanation: C(8, 3) = 8! / (3! × 5!) = (8 × 7 × 6) / (3 × 2 × 1) = 336/6 = 56.

Question 17

Mathematics · 3 marks · −1

The function f(x) = x³ − 3x + 2 has a local maximum at:

  1. A.x = 0
  2. B.x = 1
  3. C.x = −1
  4. D.x = 2

Correct answer: C

Explanation: f'(x) = 3x² − 3 = 3(x − 1)(x + 1). Critical points: x = ±1. f''(x) = 6x. f''(−1) = −6 < 0 (local maximum), f''(1) = 6 > 0 (local minimum).

Question 18

Mathematics · 3 marks · −1

If a⃗ = 2î + 3ĵ − k̂ and b⃗ = î − ĵ + 2k̂, the cross product a⃗ × b⃗ is:

  1. A.5î − 5ĵ − 5k̂
  2. B.5î + 5ĵ + 5k̂
  3. C.î + 5ĵ + 5k̂
  4. D.5î − 5ĵ + 5k̂

Correct answer: A

Explanation: a⃗ × b⃗ = î(3·2 − (−1)(−1)) − ĵ(2·2 − (−1)·1) + k̂(2·(−1) − 3·1) = î(6 − 1) − ĵ(4 + 1) + k̂(−2 − 3) = 5î − 5ĵ − 5k̂.

Question 19

Mathematics · 3 marks · −1

The general solution of the differential equation dy/dx = y/x is:

  1. A.y = Cx
  2. B.y = x + C
  3. C.y = Ceˣ
  4. D.y = C/x

Correct answer: A

Explanation: Separating variables: dy/y = dx/x. Integrating both sides: ln|y| = ln|x| + C₁. Therefore y = Cx, a family of straight lines through the origin.

Question 20

Mathematics · 3 marks · −1

A card is drawn at random from a standard deck of 52 cards. The probability of drawing a king is:

  1. A.1/13
  2. B.1/52
  3. C.4/13
  4. D.1/4

Correct answer: A

Explanation: A standard deck has 4 kings among 52 cards. P(king) = 4/52 = 1/13.

Question 21

Physics · 3 marks · −1

A ball is thrown vertically upward with velocity 20 m/s. The maximum height reached is (g = 10 m/s²):

  1. A.10 m
  2. B.20 m
  3. C.40 m
  4. D.2 m

Correct answer: B

Explanation: At maximum height, the final velocity v = 0. Using v² = u² − 2gh: 0 = (20)² − 2(10)h, so h = 400/20 = 20 m.

Question 22

Physics · 3 marks · −1

A body of mass 2 kg moving at 10 m/s is brought to rest by a constant force in 4 seconds. The instantaneous power delivered by the force at t = 2 s is:

  1. A.25 W
  2. B.50 W
  3. C.12.5 W
  4. D.100 W

Correct answer: A

Explanation: Deceleration a = 10/4 = 2.5 m/s². Force F = ma = 2 × 2.5 = 5 N. At t = 2 s, velocity = 10 − 2.5(2) = 5 m/s. Power = F × v = 5 × 5 = 25 W.

Question 23

Physics · 3 marks · −1

Three capacitors of 2 μF, 3 μF, and 6 μF are connected in series. The equivalent capacitance is:

  1. A.11 μF
  2. B.1 μF
  3. C.6 μF
  4. D.0.5 μF

Correct answer: B

Explanation: For capacitors in series: 1/C_eq = 1/2 + 1/3 + 1/6 = 3/6 + 2/6 + 1/6 = 6/6 = 1. Therefore C_eq = 1 μF.

Question 24

Physics · 3 marks · −1

Rapid compression of gas in an insulated container is an example of:

  1. A.An isothermal process
  2. B.An adiabatic process
  3. C.An isobaric process
  4. D.An isochoric process

Correct answer: B

Explanation: An adiabatic process involves no heat exchange with the surroundings (Q = 0). Rapid compression in an insulated container satisfies both conditions: the insulation prevents conduction, and rapidity prevents heat transfer.

Question 25

Physics · 3 marks · −1

A concave mirror produces a real, inverted, and same-size image when the object is placed at:

  1. A.The focus
  2. B.The center of curvature
  3. C.Between F and C
  4. D.Beyond C

Correct answer: B

Explanation: When an object is placed at the center of curvature (C) of a concave mirror, the image is formed at C itself, real, inverted, and of the same size (magnification = −1).

Question 26

Physics · 3 marks · −1

The de Broglie wavelength of an electron accelerated through a potential difference V is proportional to:

  1. A.V
  2. B.√V
  3. C.1/√V
  4. D.1/V

Correct answer: C

Explanation: The kinetic energy is eV = p²/(2m), so p = √(2meV). The de Broglie wavelength λ = h/p = h/√(2meV), which is proportional to 1/√V.

Question 27

Aptitude (Reasoning) · 3 marks · −1

All teachers are graduates. Some graduates are engineers. Which of the following conclusions is valid?

  1. A.All teachers are engineers
  2. B.Some teachers may be engineers
  3. C.No teacher is an engineer
  4. D.All engineers are teachers

Correct answer: B

Explanation: Since all teachers are graduates and some graduates are engineers, it is possible (but not certain) that some teachers are among the graduate-engineers. We can only say 'some teachers may be engineers.'

Question 28

Physics · 2 marks

The SI unit of electric current is:

  1. A.Volt
  2. B.Ohm
  3. C.Ampere
  4. D.Watt

Correct answer: C

Explanation: The SI unit of electric current is the ampere (A), defined as one coulomb of charge flowing past a point per second.

Question 29

Aptitude (Reasoning) · 3 marks · −1

If 3x + 7 = 22, what is the value of 6x + 14?

  1. A.30
  2. B.44
  3. C.22
  4. D.15

Correct answer: B

Explanation: Notice that 6x + 14 = 2(3x + 7) = 2 × 22 = 44. Alternatively, solving gives x = 5, so 6(5) + 14 = 44.

Question 30

Aptitude (Reasoning) · 3 marks · −1

In the sequence 2, 6, 18, 54, ..., the next term is:

  1. A.108
  2. B.162
  3. C.72
  4. D.216

Correct answer: B

Explanation: This is a geometric progression with common ratio r = 3 (each term is 3 times the previous). The next term is 54 × 3 = 162.

View all papers — NEST

Practice this paper with a timer

Attempt it online, get scored instantly, and see which subjects are costing you marks.

Start practising free