About this Class 12 Science practice test

Prepare for high-stakes school-leaving exams and competitive pre-medical or engineering filters with Class 12 Science practice. Master electrostatic calculus, organic synthesis pathways, genetics, and kinetics.

Class 12 Science Practice Test sample questions

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1. 1. Two point charges of +2 μC and +3 μC are placed 0.3 m apart in vacuum. Calculate the magnitude of the electrostatic force between them. (k = 9×10^9 N·m²/C²)

2. 2. A wire made of a material with resistivity 2×10^-6 Ω·m has a length of 2 m and a uniform cross-sectional area of 2×10^-6 m². Calculate its resistance, and the current that flows through it when it is connected across a 10 V battery.

3. 3. A straight current-carrying conductor of length 0.5 m carries a current of 5 A and is placed perpendicular to a uniform magnetic field of 0.2 T. Calculate the force experienced by the conductor.

4. 4. A circular coil of 100 turns and radius 0.05 m is held with its plane perpendicular to a magnetic field that changes uniformly from 0.2 T to 0.8 T in 0.3 s. Calculate the magnitude of the EMF induced in the coil.

5. 5. A series AC circuit contains a resistor of 30 Ω and an inductor of reactance 40 Ω, connected to an AC source of rms voltage 200 V. Calculate the impedance of the circuit and the rms current flowing through it.

6. 6. An electromagnetic wave in vacuum has a frequency of 6×10^14 Hz. Calculate its wavelength, and identify the region of the electromagnetic spectrum it belongs to. (c = 3×10^8 m/s)

7. 7. An object is placed 30 cm in front of a convex lens of focal length 10 cm. Using the lens formula, calculate the position and magnification of the image formed.

8. 8. Light of wavelength 400 nm strikes a metal surface whose work function is 2 eV. Calculate the maximum kinetic energy of the emitted photoelectrons. (h = 6.63×10^-34 J·s, c = 3×10^8 m/s, 1 eV = 1.6×10^-19 J)

9. 9. A radioactive sample has a half-life of 30 days and an initial activity of 800 disintegrations per second. Calculate its activity after 90 days.

10. 10. In a voltage regulator circuit, a Zener diode with breakdown voltage 6 V is connected in series with a 100 Ω resistor across an unregulated 10 V supply, and a load drawing 20 mA is connected across the Zener diode. Calculate the current flowing through the Zener diode.

11. 11. A metal crystallizes in a face-centred cubic (fcc) unit cell with an edge length of 400 pm. Calculate the radius of the metal atom.

12. 12. 6 g of urea (molar mass 60 g/mol) is dissolved in 500 g of water. Calculate the depression in the freezing point of the solution. (Kf of water = 1.86 K·kg/mol)

13. 13. For the cell reaction Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s), the standard cell potential is 1.10 V. Using the Nernst equation, calculate the cell EMF at 298 K when [Zn2+] = 0.1 M and [Cu2+] = 0.01 M.

14. 14. In a certain reaction, doubling the concentration of reactant A (with B constant) doubles the rate, while doubling the concentration of reactant B (with A constant) increases the rate four-fold. Determine the order of the reaction with respect to A, with respect to B, and the overall order.

15. 15. Write the IUPAC name of the coordination compound [Co(NH3)5Cl]Cl2, and determine the oxidation state of cobalt in it.

16. 16. Explain why chlorobenzene undergoes nucleophilic substitution reactions much less readily than chloroethane.

17. 17. Arrange propane, dimethyl ether, and ethanol (all of similar molar mass) in increasing order of boiling point, and briefly justify the order.

18. 18. Between acetic acid (CH3COOH) and chloroacetic acid (ClCH2COOH), which is the stronger acid, and why?

19. 19. Explain why aniline is a weaker base than ethylamine.

20. 20. Identify the type of glycosidic linkage between glucose and fructose in sucrose, and state whether sucrose is a reducing or non-reducing sugar.

21. 21. Hydra reproduces asexually by one method, and Amoeba by another. Name the specific type of asexual reproduction shown by each.

22. 22. In angiosperms, one male gamete fuses with the egg cell to form the zygote, while the second male gamete fuses with the two polar nuclei. What is this second fusion event called, and what is the ploidy of the resulting nucleus?

23. 23. In a typical 28-day human menstrual cycle with ovulation around day 14, if fertilization does not occur, approximately when does menstruation begin, and which hormonal change triggers it?

24. 24. In a dihybrid cross between two pea plants heterozygous for seed shape and seed color (RrYy × RrYy), what is the expected phenotypic ratio of the offspring, and what fraction is expected to show both recessive traits (wrinkled, green)?

25. 25. Explain why the sex of a human child is determined by the father's contribution, and state the probability of having a male child in any given pregnancy.

26. 26. Given the DNA template strand 3'-TACGCATG-5', write the sequence of the mRNA transcribed from it.

27. 27. Name the pathogen and the vector responsible for malaria, and explain what causes the recurring chills and fever seen in infected patients.

28. 28. Streptomycin, a widely used antibiotic, is obtained from a soil microorganism. Name this microorganism and state whether it is classified as a bacterium or a fungus.

29. 29. Name the restriction endonuclease that recognizes and cuts the palindromic sequence GAATTC, and briefly describe how recombinant DNA technology is used to produce human insulin.

30. 30. A bacterial population grows exponentially with a growth rate constant (r) of 0.1 per hour, starting from 100 cells. Using Nt = N0 * e^(rt), calculate the population after 10 hours. (e ≈ 2.718)

Answer key & quick explanations

Short answers for the sample questions above. Use this to self-check before generating a fresh AI-built mock test.

1. 1. Two point charges of +2 μC and +3 μC are placed 0.3 m apart in vacuum. Calculate the magnitude of the electrostatic force between them. (k = 9×10^9 N·m²/C²)

   0.6 N (repulsive)

   F = k·q1·q2/r² = (9×10^9 × 2×10^-6 × 3×10^-6)/(0.3)² = 0.054/0.09 = 0.6 N. Since both charges are positive, the force is repulsive.

2. 2. A wire made of a material with resistivity 2×10^-6 Ω·m has a length of 2 m and a uniform cross-sectional area of 2×10^-6 m². Calculate its resistance, and the current that flows through it when it is connected across a 10 V battery.

   R = 2 Ω, I = 5 A

   R = ρL/A = (2×10^-6 × 2)/(2×10^-6) = 2 Ω. By Ohm's law, I = V/R = 10/2 = 5 A.

3. 3. A straight current-carrying conductor of length 0.5 m carries a current of 5 A and is placed perpendicular to a uniform magnetic field of 0.2 T. Calculate the force experienced by the conductor.

   0.5 N

   F = BIL sinθ with θ = 90°, so F = BIL = 0.2 × 5 × 0.5 = 0.5 N.

4. 4. A circular coil of 100 turns and radius 0.05 m is held with its plane perpendicular to a magnetic field that changes uniformly from 0.2 T to 0.8 T in 0.3 s. Calculate the magnitude of the EMF induced in the coil.

   ≈1.57 V

   EMF = N·A·(dB/dt), where A = πr² = π(0.05)² ≈ 0.00785 m² and dB/dt = (0.8−0.2)/0.3 = 2 T/s. EMF = 100 × 0.00785 × 2 ≈ 1.57 V.

5. 5. A series AC circuit contains a resistor of 30 Ω and an inductor of reactance 40 Ω, connected to an AC source of rms voltage 200 V. Calculate the impedance of the circuit and the rms current flowing through it.

   Z = 50 Ω, I = 4 A

   Z = √(R² + XL²) = √(30² + 40²) = √2500 = 50 Ω. rms current I = V/Z = 200/50 = 4 A.

6. 6. An electromagnetic wave in vacuum has a frequency of 6×10^14 Hz. Calculate its wavelength, and identify the region of the electromagnetic spectrum it belongs to. (c = 3×10^8 m/s)

   500 nm; visible light (green region)

   λ = c/f = (3×10^8)/(6×10^14) = 5×10^-7 m = 500 nm, which lies within the visible spectrum, specifically the green region.

7. 7. An object is placed 30 cm in front of a convex lens of focal length 10 cm. Using the lens formula, calculate the position and magnification of the image formed.

   v = +15 cm (real image), m = -0.5

   Using 1/v − 1/u = 1/f with u = −30 cm, f = +10 cm: 1/v = 1/10 − 1/30 = 1/15, so v = 15 cm. Magnification m = v/u = 15/(−30) = −0.5, so the image is real, inverted, and diminished to half the object's size.

8. 8. Light of wavelength 400 nm strikes a metal surface whose work function is 2 eV. Calculate the maximum kinetic energy of the emitted photoelectrons. (h = 6.63×10^-34 J·s, c = 3×10^8 m/s, 1 eV = 1.6×10^-19 J)

   ≈1.11 eV

   Photon energy E = hc/λ = (6.63×10^-34 × 3×10^8)/(400×10^-9) ≈ 4.97×10^-19 J ≈ 3.11 eV. By Einstein's photoelectric equation, KEmax = E − φ = 3.11 − 2 = 1.11 eV.

9. 9. A radioactive sample has a half-life of 30 days and an initial activity of 800 disintegrations per second. Calculate its activity after 90 days.

   100 disintegrations per second

   90 days corresponds to 3 half-lives, so activity = 800/(2³) = 800/8 = 100 dps.

10. 10. In a voltage regulator circuit, a Zener diode with breakdown voltage 6 V is connected in series with a 100 Ω resistor across an unregulated 10 V supply, and a load drawing 20 mA is connected across the Zener diode. Calculate the current flowing through the Zener diode.

    20 mA

    Total current from the supply = (Vin − Vz)/R = (10−6)/100 = 40 mA. This current splits between the Zener diode and the load, so Zener current = 40 − 20 = 20 mA.

11. 11. A metal crystallizes in a face-centred cubic (fcc) unit cell with an edge length of 400 pm. Calculate the radius of the metal atom.

    ≈141.4 pm

    In an fcc lattice atoms touch along the face diagonal, so 4r = √2·a, giving r = (√2/4) × 400 ≈ 141.4 pm.

12. 12. 6 g of urea (molar mass 60 g/mol) is dissolved in 500 g of water. Calculate the depression in the freezing point of the solution. (Kf of water = 1.86 K·kg/mol)

    0.372 K (°C)

    Moles of urea = 6/60 = 0.1 mol; molality = 0.1 mol/0.5 kg = 0.2 mol/kg. Since urea is a non-electrolyte (i = 1), ΔTf = Kf × m = 1.86 × 0.2 = 0.372 K.

13. 13. For the cell reaction Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s), the standard cell potential is 1.10 V. Using the Nernst equation, calculate the cell EMF at 298 K when [Zn2+] = 0.1 M and [Cu2+] = 0.01 M.

    ≈1.07 V

    E = E° − (0.0591/n)log([Zn2+]/[Cu2+]), n = 2. log(0.1/0.01) = log(10) = 1, so E = 1.10 − (0.0591/2)(1) = 1.10 − 0.0296 ≈ 1.07 V.

14. 14. In a certain reaction, doubling the concentration of reactant A (with B constant) doubles the rate, while doubling the concentration of reactant B (with A constant) increases the rate four-fold. Determine the order of the reaction with respect to A, with respect to B, and the overall order.

    Order wrt A = 1, order wrt B = 2, overall order = 3

    Rate ∝ [A]^m[B]^n. Doubling [A] doubles rate → 2^m = 2 → m = 1. Doubling [B] quadruples rate → 2^n = 4 → n = 2. Overall order = m + n = 3.

15. 15. Write the IUPAC name of the coordination compound [Co(NH3)5Cl]Cl2, and determine the oxidation state of cobalt in it.

    Pentaamminechloridocobalt(III) chloride; Co is +3

    The two ionizable Cl⁻ ions outside the coordination sphere give the complex ion [Co(NH3)5Cl]2+ a charge of +2. Since NH3 is neutral and the coordinated Cl⁻ contributes −1, Co + 0 − 1 = +2, so Co = +3.

16. 16. Explain why chlorobenzene undergoes nucleophilic substitution reactions much less readily than chloroethane.

    Because resonance gives the C-Cl bond in chlorobenzene partial double-bond character, making it stronger and harder to break

    In chlorobenzene, a lone pair on chlorine is delocalized into the benzene ring by resonance, giving the C−Cl bond partial double-bond character, making it shorter, stronger, and less polar. In chloroethane the C−Cl bond is a simple, more polar sigma bond that nucleophiles attack easily, so it reacts far more readily.

17. 17. Arrange propane, dimethyl ether, and ethanol (all of similar molar mass) in increasing order of boiling point, and briefly justify the order.

    propane < dimethyl ether < ethanol

    Propane is non-polar with only weak van der Waals forces (lowest bp); dimethyl ether is polar (dipole-dipole forces) but cannot hydrogen-bond with itself (intermediate bp); ethanol's O−H group forms intermolecular hydrogen bonds, giving it the highest boiling point.

18. 18. Between acetic acid (CH3COOH) and chloroacetic acid (ClCH2COOH), which is the stronger acid, and why?

    Chloroacetic acid is the stronger acid

    The electronegative chlorine exerts an electron-withdrawing inductive (−I) effect that stabilizes the conjugate base (chloroacetate ion) by delocalizing its negative charge, making the proton easier to lose. Acetic acid lacks this effect, so it is the weaker acid.

19. 19. Explain why aniline is a weaker base than ethylamine.

    Because aniline's nitrogen lone pair is delocalized into the benzene ring

    In aniline, the lone pair on nitrogen is involved in resonance with the aromatic ring, reducing its availability to accept a proton. In ethylamine, the nitrogen lone pair is fully localized, and the electron-donating alkyl group further increases its availability, making ethylamine the stronger base.

20. 20. Identify the type of glycosidic linkage between glucose and fructose in sucrose, and state whether sucrose is a reducing or non-reducing sugar.

    α,β-1,2-glycosidic linkage; sucrose is a non-reducing sugar

    The linkage forms between C1 of α-glucose and C2 of β-fructose, involving both anomeric carbons. Since no free anomeric (reducing) group remains, sucrose cannot reduce Fehling's or Tollens' reagent, making it a non-reducing sugar.

21. 21. Hydra reproduces asexually by one method, and Amoeba by another. Name the specific type of asexual reproduction shown by each.

    Hydra — budding; Amoeba — binary fission

    In Hydra, a bud develops as an outgrowth that grows and detaches to form a new individual (budding). In Amoeba, the parent cell simply divides into two equal daughter cells (binary fission).

22. 22. In angiosperms, one male gamete fuses with the egg cell to form the zygote, while the second male gamete fuses with the two polar nuclei. What is this second fusion event called, and what is the ploidy of the resulting nucleus?

    Triple fusion; the resulting primary endosperm nucleus is triploid (3n)

    The second male gamete (n) fuses with the two polar nuclei (n+n) in the central cell — an event called triple fusion — producing the triploid (3n) primary endosperm nucleus, which develops into the endosperm.

23. 23. In a typical 28-day human menstrual cycle with ovulation around day 14, if fertilization does not occur, approximately when does menstruation begin, and which hormonal change triggers it?

    Around day 28 (start of the next cycle); triggered by a sharp decline in progesterone (and estrogen)

    Without fertilization, the corpus luteum degenerates, causing progesterone and estrogen levels to fall sharply. This hormonal withdrawal causes the endometrial lining to break down and shed, marking the onset of menstruation around day 28.

24. 24. In a dihybrid cross between two pea plants heterozygous for seed shape and seed color (RrYy × RrYy), what is the expected phenotypic ratio of the offspring, and what fraction is expected to show both recessive traits (wrinkled, green)?

    9:3:3:1 phenotypic ratio; 1/16 show both recessive traits

    Independent assortment of the two gene pairs produces a 9:3:3:1 ratio (Round Yellow : Round green : wrinkled Yellow : wrinkled green) among 16 combinations, so the doubly recessive wrinkled-green class makes up 1/16 of the offspring.

25. 25. Explain why the sex of a human child is determined by the father's contribution, and state the probability of having a male child in any given pregnancy.

    The father's sperm determines sex (X-bearing → female, Y-bearing → male); probability of a male child = 1/2

    Human females are XX and produce only X-bearing eggs, while males are XY and produce equal numbers of X-bearing and Y-bearing sperm. Fertilization by an X-sperm gives XX (female) offspring, and by a Y-sperm gives XY (male) offspring, so each pregnancy has a 1/2 probability of being male.

26. 26. Given the DNA template strand 3'-TACGCATG-5', write the sequence of the mRNA transcribed from it.

    5'-AUGCGUAC-3'

    RNA polymerase reads the template 3'→5' and synthesizes a complementary, antiparallel mRNA strand 5'→3', pairing A-U, T-A, G-C, C-G (using U instead of T): template T-A-C-G-C-A-T-G gives mRNA A-U-G-C-G-U-A-C.

27. 27. Name the pathogen and the vector responsible for malaria, and explain what causes the recurring chills and fever seen in infected patients.

    Pathogen: Plasmodium (protozoan); Vector: female Anopheles mosquito; chills/fever are caused by rupture of infected RBCs

    The Plasmodium parasite, transmitted by the bite of a female Anopheles mosquito, multiplies inside red blood cells; periodic rupture of infected RBCs releases merozoites and toxic metabolic products into the bloodstream, producing the characteristic cyclical chills and fever.

28. 28. Streptomycin, a widely used antibiotic, is obtained from a soil microorganism. Name this microorganism and state whether it is classified as a bacterium or a fungus.

    Streptomyces griseus; it is a bacterium (an actinomycete)

    Streptomyces griseus is a filamentous, soil-dwelling actinomycete bacterium; despite its fungus-like filamentous growth, it is classified as a bacterium, and it is the natural source of the antibiotic streptomycin.

29. 29. Name the restriction endonuclease that recognizes and cuts the palindromic sequence GAATTC, and briefly describe how recombinant DNA technology is used to produce human insulin.

    EcoRI; the human insulin gene is inserted into a bacterial plasmid vector and expressed in E. coli

    EcoRI recognizes the palindromic sequence GAATTC and cuts between the G and A on each strand, leaving sticky ends useful for cloning. In insulin production, DNA sequences coding for the insulin A and B chains are inserted into plasmid vectors, introduced into E. coli, which expresses the chains; these are extracted and combined via disulfide bonds to form functional human insulin.

30. 30. A bacterial population grows exponentially with a growth rate constant (r) of 0.1 per hour, starting from 100 cells. Using Nt = N0 * e^(rt), calculate the population after 10 hours. (e ≈ 2.718)

    ≈272 cells

    Nt = N0·e^(rt) = 100 × e^(0.1×10) = 100 × e¹ ≈ 100 × 2.718 ≈ 271.8, so about 272 cells.

Curriculum Mapping & Learning Guide

Use this breakdown to identify which skills each question tests and guide post-test review.

Class 12 Science chapters covered

1. Chapter 1: Electrostatics & Current Electricity: Coulomb's law, resistivity, and circuit calculations.
2. Chapter 2: Magnetism, EMI, AC & Modern Physics: Induced EMF, impedance, optics, and the photoelectric effect.
3. Chapter 3: Solid State, Solutions & Electrochemistry: Unit cells, colligative properties, and the Nernst equation.
4. Chapter 4: Chemical Kinetics & Coordination Compounds: Rate laws and IUPAC naming.
5. Chapter 5: Organic Chemistry: Reactivity, acidity, basicity, and biomolecules.
6. Chapter 6: Reproduction, Genetics & Biotechnology: Mendelian genetics, molecular biology, and applications.
7. Chapter 7: Human Welfare & Ecology: Diseases, antibiotics, and population growth.

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