NEET 2027 · Full Syllabus Practice · Aamirah Fathima
Answer Key & Solutions — Set 4
Quick-reference grid first, then a one-line reason for every question with its topic tag. Score the paper, then re-work every wrong answer before moving on.
Questions
180
Max marks
720
Correct
+4
Wrong
−1
Set
4
Quick key
All 180 answers
001 D
002 B
003 A
004 C
005 B
006 B
007 C
008 B
009 B
010 C
011 B
012 B
013 B
014 C
015 B
016 B
017 B
018 C
019 B
020 A
021 B
022 B
023 B
024 B
025 B
026 B
027 C
028 B
029 B
030 B
031 B
032 A
033 B
034 B
035 B
036 B
037 B
038 B
039 B
040 A
041 B
042 B
043 B
044 B
045 B
046 B
047 C
048 B
049 A
050 A
051 B
052 B
053 A
054 B
055 B
056 B
057 B
058 C
059 B
060 A
061 C
062 C
063 B
064 B
065 A
066 B
067 B
068 C
069 B
070 B
071 B
072 C
073 B
074 B
075 B
076 B
077 B
078 B
079 B
080 B
081 A
082 A
083 B
084 A
085 A
086 B
087 B
088 B
089 C
090 B
091 B
092 C
093 B
094 B
095 B
096 C
097 B
098 A
099 B
100 C
101 B
102 B
103 C
104 B
105 B
106 B
107 B
108 C
109 C
110 B
111 B
112 B
113 B
114 C
115 B
116 B
117 B
118 B
119 B
120 B
121 B
122 B
123 A
124 B
125 B
126 C
127 B
128 C
129 C
130 B
131 B
132 B
133 B
134 B
135 B
136 B
137 B
138 B
139 C
140 A
141 B
142 D
143 D
144 B
145 B
146 B
147 A
148 A
149 B
150 B
151 B
152 B
153 B
154 B
155 B
156 B
157 B
158 A
159 D
160 C
161 B
162 B
163 B
164 B
165 B
166 B
167 B
168 B
169 B
170 B
171 A
172 B
173 B
174 B
175 B
176 C
177 B
178 B
179 B
180 B
Physics
Section A · worked reasoning
Q001 (D) Watt
The watt is a unit of power, that is energy per unit time.
Units & Dimensions
Q002 (B) Systematic error
An instrumental zero error shifts every reading in the same direction, so it is systematic.
Errors & Significant Figures
Q003 (A) πr and 2r
Half the circumference is πr, while the displacement is the diameter 2r.
Kinematics
Q004 (C) Is independent of the horizontal speed
Vertical and horizontal motions are independent; time depends only on the height.
Kinematics
Q005 (B) Equal to the applied force
Static friction is self-adjusting and just balances the applied force until the limit is reached.
Laws of Motion
Q006 (B) √(gr)
At the top, gravity supplies the centripetal force: mg = mv²/r ⇒ v = √(gr).
Laws of Motion
Q007 (C) 22 J
W = F·d = 5×2 + 3×4 = 22 J.
Work, Energy & Power
Q008 (B) Zero
Work by a conservative force depends only on the end points, which coincide for a closed path.
Work, Energy & Power
Q009 (B) Zero
τ = rF sinθ vanishes because the perpendicular distance from the axis is zero.
Rotational Motion
Q010 (C) (7/5)MR²
Parallel axis theorem: (2/5)MR² + MR² = (7/5)MR².
Rotational Motion
Q011 (B) −Gm₁m₂/r
The negative sign shows the bound nature of the gravitational interaction.
Gravitation
Q012 (B) The station and astronaut are both in free fall with the same acceleration
There is no normal reaction between the astronaut and the floor during free fall.
Gravitation
Q013 (B) Smaller strain and hence a larger Young's modulus
Elasticity is measured by the resistance to deformation, that is by Y = stress/strain.
Elasticity
Q014 (C) 2000 N
Pascal's law gives F₂ = F₁ × (A₂/A₁) = 20 × 100 = 2000 N.
Fluids
Q015 (B) Reynolds number
Flow is generally streamline below Re ≈ 1000 and turbulent above Re ≈ 2000.
Fluids
Q016 (B) Decreases
λ_m T = constant, so a hotter body radiates most strongly at a shorter wavelength.
Thermal Properties
Q017 (B) No heat engine can have 100% efficiency
Some heat must always be rejected to the sink; complete conversion of heat into work is impossible.
Thermodynamics
Q018 (C) Zero
Internal energy of an ideal gas depends only on temperature, which stays constant.
Thermodynamics
Q019 (B) Inversely proportional to the number density
λ = 1/(√2 nπd²), so denser gases have shorter mean free paths.
Kinetic Theory
Q020 (A) C_p − C_v = R
Mayer's relation follows from the extra work done in expansion at constant pressure.
Kinetic Theory
Q021 (B) Decreases exponentially with time
The dissipative force makes the amplitude fall off as e^(−bt/2m).
Oscillations
Q022 (B) √6 times
T ∝ 1/√g, so a smaller g lengthens the period by a factor of √6.
Oscillations
Q023 (B) Longitudinal and cannot be polarised
Air cannot sustain shear, so sound propagates as compressions and rarefactions.
Waves
Q024 (B) Decreases
Relative separation increases, so fewer wavefronts reach the observer per second.
Waves
Q025 (B) Charge exists only as an integral multiple of e
q = ne where n is an integer and e = 1.6 × 10⁻¹⁹ C.
Electrostatics
Q026 (B) σ/2ε₀ and independent of distance
Gauss's law gives a uniform field on either side of the sheet.
Electrostatics
Q027 (C) 5 μF
Capacitances simply add in parallel.
Capacitors
Q028 (B) Greater than the emf
V = E + Ir when current is driven into the cell.
Current Electricity
Q029 (B) Increases
Increased lattice vibrations shorten the relaxation time of the electrons.
Current Electricity
Q030 (B) μ₀I/4R
A semicircle contributes half the field of a full loop, μ₀I/2R.
Moving Charges & Magnetism
Q031 (B) The net current enclosed by the loop
∮B·dl = μ₀I_enclosed.
Moving Charges & Magnetism
Q032 (A) 0°
The earth's field is horizontal at the magnetic equator and vertical at the poles.
Magnetism & Matter
Q033 (B) ½LI²
U = ½LI², analogous to ½CV² for a capacitor.
Electromagnetic Induction
Q034 (B) NABω
ε = NABω sin ωt, so the peak value is NABω.
Electromagnetic Induction
Q035 (B) 159 Hz
f = 1/(2π√LC) = 1/(2π × 10⁻³) ≈ 159 Hz.
Alternating Current
Q036 (B) Reduces current without dissipating power
An ideal inductor is wattless, so no energy is wasted as heat.
Alternating Current
Q037 (B) A time varying electric field
Maxwell added the term ε₀ dΦ_E/dt to make Ampere's law consistent.
Electromagnetic Waves
Q038 (B) Total internal reflection
Light repeatedly undergoes total internal reflection at the core–cladding boundary.
Ray Optics
Q039 (B) A concave lens
A diverging lens shifts the image from in front of the retina onto it.
Ray Optics
Q040 (A) A source of secondary wavelets
The new wavefront is the forward envelope of these secondary wavelets.
Wave Optics
Q041 (B) Half
β = λD/d, so β is inversely proportional to the slit separation.
Wave Optics
Q042 (B) The number of photoelectrons emitted per second
Intensity determines the number of photons, not the energy of each photon.
Dual Nature of Matter
Q043 (B) A small dense positively charged nucleus
A few alpha particles bouncing back showed that positive charge is concentrated in a tiny volume.
Atoms
Q044 (B) Reverse bias
Reverse bias makes the fractional change in current with illumination easy to measure.
Semiconductors
Q045 (B) Electrons and holes recombine near the junction under forward bias
Recombination releases energy as photons of energy nearly equal to the band gap.
Semiconductors
Chemistry
Section B · worked reasoning
Q046 (B) 0.5
One mole of any gas occupies 22.4 L at STP.
Some Basic Concepts
Q047 (C) 35%
Two N atoms give 28 out of a molar mass of 80 ⇒ 35%.
Some Basic Concepts
Q048 (B) Isobars
For example ¹⁴C and ¹⁴N are isobars.
Structure of Atom
Q049 (A) Δx · Δp ≥ h/4π
Position and momentum cannot both be determined with arbitrary precision.
Structure of Atom
Q050 (A) Na > Mg > Al > Si
Atomic radius decreases across a period as effective nuclear charge increases.
Classification & Periodicity
Q051 (B) Diagonal relationship
The first element of a group resembles the second element of the next group.
Classification & Periodicity
Q052 (B) sp³d, trigonal bipyramidal
Five bond pairs around phosphorus give a trigonal bipyramidal shape with axial bonds longer.
Chemical Bonding
Q053 (A) C≡C < C=C < C–C
More shared electron pairs pull the nuclei closer, so a triple bond is shortest.
Chemical Bonding
Q054 (B) Resonance
The real structure is a resonance hybrid of three equivalent canonical forms.
Chemical Bonding
Q055 (B) Intramolecular hydrogen bonding
Chelation within the molecule prevents association between molecules.
Chemical Bonding
Q056 (B) Zero
ΔG = 0 defines the position of equilibrium at constant T and P.
Thermodynamics
Q057 (B) The reaction is always between H⁺ and OH⁻ to form water
Both are completely ionised, so the only reaction is H⁺ + OH⁻ → H₂O.
Thermodynamics
Q058 (C) Does not shift the equilibrium but helps it to be attained faster
A catalyst speeds up forward and backward reactions equally.
Equilibrium
Q059 (B) 2
[H⁺] = 10⁻² M ⇒ pH = 2.
Equilibrium
Q060 (A) An acid because it accepts an electron pair
The electron-deficient boron atom acts as an electron pair acceptor.
Equilibrium
Q061 (C) Zinc is the reducing agent
Zn loses electrons, so it is oxidised and acts as the reducing agent.
Redox Reactions
Q062 (C) Free radicals
Each atom retains one electron of the shared pair.
Organic Chemistry – Basic Principles
Q063 (B) Position isomers
They differ only in the position of the hydroxyl group on the same chain.
Organic Chemistry – Basic Principles
Q064 (B) Crystallisation
The impure solid is dissolved hot and allowed to crystallise on cooling.
Organic Chemistry – Basic Principles
Q065 (A) Ethane
Sabatier–Senderens reduction adds hydrogen across the double bond.
Hydrocarbons
Q066 (B) Cold dilute alkaline KMnO₄
The purple colour is discharged as the alkene is converted into a vicinal diol.
Hydrocarbons
Q067 (B) Benzoic acid
The side chain is oxidised completely to the carboxylic acid.
Hydrocarbons
Q068 (C) Molality
Molality is based on the mass of solvent, which does not change with temperature.
Solutions
Q069 (B) The molality of the solution
ΔT_f = K_f m, a colligative property.
Solutions
Q070 (B) Maintain electrical neutrality and complete the circuit
It allows ion migration between the half cells without mixing the solutions.
Electrochemistry
Q071 (B) Applying Kohlrausch's law of independent migration of ions
Λm° values of strong electrolytes are combined to obtain that of the weak electrolyte.
Electrochemistry
Q072 (C) 4
Overall order is two, so the rate becomes 2 × 2 = 4 times.
Chemical Kinetics
Q073 (B) Roughly doubles the rate
The temperature coefficient of most reactions is about 2 to 3.
Chemical Kinetics
Q074 (B) 1.73 BM
μ = √(n(n + 2)) with n = 1 gives √3 = 1.73 BM.
d- and f-Block Elements
Q075 (B) Strong metallic bonding involving d electrons
Unpaired d electrons contribute to interatomic bonding in the metallic lattice.
d- and f-Block Elements
Q076 (B) Charge transfer from oxygen to manganese
Mn in MnO₄⁻ is d⁰, so the colour must come from a ligand to metal charge transfer.
d- and f-Block Elements
Q077 (B) Coordination number
Primary valency is satisfied by negative ions and secondary valency by ligands.
Coordination Compounds
Q078 (B) d²sp³, 3
Cr³⁺ is 3d³; the three electrons stay unpaired in t₂g and inner d orbitals are used.
Coordination Compounds
Q079 (B) cis-[Pt(NH₃)₂Cl₂]
Only the cis isomer of diamminedichloridoplatinum(II) is therapeutically active.
Coordination Compounds
Q080 (B) A racemic mixture
The planar carbocation intermediate can be attacked from either face.
Haloalkanes & Haloarenes
Q081 (A) NaI in dry acetone
Sodium chloride precipitates in acetone, driving the equilibrium towards the iodide.
Haloalkanes & Haloarenes
Q082 (A) A primary alcohol
Formaldehyde is the only aldehyde that yields a primary alcohol with RMgX.
Alcohols, Phenols & Ethers
Q083 (B) Salicylaldehyde
Treatment with CHCl₃ and aqueous NaOH introduces a –CHO group at the ortho position.
Alcohols, Phenols & Ethers
Q084 (A) Ethanal and propanone
Aliphatic aldehydes give a red precipitate of Cu₂O; ketones do not react.
Aldehydes, Ketones & Carboxylic Acids
Q085 (A) 3-Hydroxybutanal
The β-hydroxy aldehyde formed can lose water on heating to give but-2-enal.