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Class 12 is one of the most important years students go through in their student life. The concepts that are studied by the students in their class 12 possess great significance. These concepts are used by the students in competitive examinations like JEE, NEET, or CA and bachelor’s degrees as well.
Practicing the questions with different difficulty levels consolidates your concepts and helps you achieve your desired score with flying colors.
In the table given below, we have provided the links to downloadable PDFs of important questions of class 12, you can now download the PDFs and ace your examination.
Class 12 Biology Important Questions
Class 12 Business Studies Important Questions
Class 12 Chemistry Important Questions
We hope that you benefit from the important questions provided above and achieve an overwhelming victory in your examinations.
Important questions provide extra help and work as important reference material to prepare well for exams. Don’t rely solely on important questions, just use them as extra study material for class 12 board preparations.
1. Derive the expression for drift velocity of electrons in a conductor and relate it with current.
Answer: When a potential difference is applied across a conductor, free electrons move towards the positive end with a small average velocity called drift velocity. If I is current, n is number of electrons per unit volume, A is cross-sectional area, and e is the charge of an electron,
then I = nAe v_d.
Hence, drift velocity v_d = I / (nAe).
It depends on the electric field and relaxation time: v_d = (eEτ)/m.
This explains how current in a metal arises due to electron motion.
2. Explain the principle of a potentiometer and how it can be used to compare two emf values.
Answer: A potentiometer is based on the principle that potential drop along a uniform wire is directly proportional to its length. If E1 and E2 are two cells balanced at lengths L1 and L2, then E1/E2 = L1/L2.
It gives accurate comparison as no current flows through the cells during balancing.
3. What is the condition for resonance in an LCR circuit? What happens at resonance?
Answer: Resonance occurs when inductive reactance equals capacitive reactance (XL = XC).
At this point, the impedance of the circuit is minimum and current becomes maximum.
The resonant frequency is f = 1 / (2π√(LC)).
At resonance, voltage and current are in phase.
4. Explain how electromagnetic waves are produced and write their characteristics.
Answer: A changing electric field produces a magnetic field, and a changing magnetic field produces an electric field. These time-varying fields sustain each other and propagate as electromagnetic waves. They travel at the speed of light (3 × 10⁸ m/s), are transverse in nature, and do not need a medium.
5. What is polarization of light? How does it prove that light is transverse in nature?
Answer: Polarization means restricting the vibrations of light to one plane only. Unpolarized light vibrates in all planes perpendicular to the direction of propagation. When light passes through a Polaroid, vibrations in all other directions are blocked.
This confirms that light waves are transverse.
6. Explain the working of a transistor as an amplifier.
Answer: In an amplifier circuit, a small input voltage is applied to the base-emitter junction.
Due to transistor action, a large change in collector current occurs.
This produces a larger voltage across the load resistor in the collector circuit.
Thus, the transistor amplifies the signal ,output power is greater than input power.
7. State Einstein’s photoelectric equation and explain its significance.
Answer: Einstein’s photoelectric equation:
Energy of photon = Work function + Kinetic energy of emitted electron.
hν = φ + ½mv².
This equation shows that light consists of discrete packets of energy (photons) and explains the threshold frequency concept.
8. Define nuclear fission and nuclear fusion with examples.
Answer:
9. What is the difference between interference and diffraction of light?
Answer:
10. Explain the principle of a transformer and derive the relation between input and output voltages.
Answer: A transformer works on electromagnetic induction and mutual inductance between two coils. The primary coil is connected to an AC source; the changing current produces magnetic flux linking the secondary coil.
If Np and Ns are turns, and Vp and Vs are voltages, then: Vp/Vs = Np/Ns.
Step-up transformers increase voltage; step-down transformers decrease it.
1. Explain the law of chemical equilibrium and derive the expression for equilibrium constant.
Answer: For a reversible reaction aA + bB ⇌ cC + dD,
Kc = [C]^c [D]^d / [A]^a [B]^b.
At equilibrium, rate of forward reaction equals rate of backward reaction.
Kc is constant at a given temperature and depends only on temperature.
2. What is the difference between order and molecularity of a reaction?
Answer: Order = sum of powers of concentration terms in rate law (experimental).
Molecularity = number of molecules colliding in a single reaction step (theoretical).
Order can be zero or fractional; molecularity is always whole and positive.
3. Define adsorption and distinguish between physical and chemical adsorption.
Answer: Adsorption is the accumulation of particles on a surface. Physical adsorption: weak van der Waals forces, low enthalpy, reversible. Chemical adsorption: strong chemical bonds, high enthalpy, often irreversible.
4. Explain the process of corrosion and methods to prevent it.
Answer: Corrosion is the slow destruction of metals due to chemical or electrochemical reactions with the environment.
Example: rusting of iron due to oxidation.
Prevention methods: painting, galvanization, cathodic protection, or alloying.
5. Describe the preparation and properties of KMnO4.
Answer: Prepared from pyrolusite (MnO2) by fusion with KOH and oxidation with Cl2.
KMnO4 is a strong oxidizing agent in both acidic and alkaline media.
Used in titrations, bleaching, and as disinfectant.
6. Explain the hybridization and shape of the SF6 molecule.
Answer: In SF6, the central S atom undergoes sp³d² hybridization. Six orbitals form six sigma bonds with fluorine atoms.
Geometry: octahedral, bond angle 90°.
7. State and explain Kohlrausch’s Law.
Answer: The molar conductivity of an electrolyte at infinite dilution is the sum of the ionic conductivities of its cations and anions.
Λ°m = λ°+ + λ°–.
This law helps in calculating the degree of dissociation and weak electrolyte conductance.
8. What are lanthanoids? Mention two of their characteristics.
Answer: Lanthanoids are 14 elements following lanthanum (atomic numbers 58–71). They show similar chemical properties, mainly +3 oxidation state, and gradual decrease in atomic and ionic size (lanthanoid contraction).
9. What is the difference between DNA and RNA structurally and functionally?
Answer: DNA has deoxyribose sugar and double helix structure; RNA has ribose sugar and single strand. DNA stores genetic information; RNA helps in protein synthesis.
10. Explain the role of enzymes as biocatalysts.
Answer: Enzymes speed up biochemical reactions without being consumed. They lower activation energy by forming enzyme-substrate complexes.
Example: Amylase converts starch to sugar.
1. Explain the process of transcription in DNA.
Answer: Transcription is the process of synthesizing RNA from a DNA template. RNA polymerase binds to the promoter region, unwinds DNA, and adds complementary RNA nucleotides until a terminator sequence is reached. The mRNA then detaches and moves for translation.
2. Describe the structure and function of the nephron.
Answer: A nephron is the structural and functional unit of the kidney. It consists of Bowman’s capsule, glomerulus, PCT, loop of Henle, and DCT. It filters blood, reabsorbs useful substances, and removes wastes as urine.
3. Explain the mechanism of photosynthesis in plants.
Answer: Photosynthesis occurs in chloroplasts. Light reactions (in thylakoids) produce ATP and NADPH. Dark reactions (in stroma, Calvin cycle) use ATP and NADPH to fix CO2 into glucose. Overall equation: 6CO2 + 6H2O → C6H12O6 + 6O2.
4. What is the difference between mitosis and meiosis?
Answer: Mitosis: one division, two identical cells, same chromosome number. Meiosis: two divisions, four haploid cells, half chromosome number. Mitosis for growth; meiosis for gamete formation.
5. Describe the structure of a human heart.
Answer: Four chambers - right atrium, right ventricle, left atrium, left ventricle. Valves prevent backflow. The right side pumps deoxygenated blood to the lungs, the left side pumps oxygenated blood to the body.
6. Explain the process of fertilization in flowering plants.
Answer: Pollen grains germinate on stigma, pollen tube grows to ovule, two male gametes released: one fuses with egg (zygote), other with secondary nucleus (endosperm). This is called double fertilization.
7. What is the difference between innate and acquired immunity?
Answer: Innate: present from birth, non-specific. Acquired: developed after exposure, specific to pathogens. Involves antibodies and memory cells.
8. What is biotechnology? Mention two of its applications.
Answer: Use of living organisms for human welfare. Applications: Production of insulin by recombinant DNA, genetically modified crops (Bt cotton).
9. Explain the carbon cycle briefly.
Answer: CO2 is absorbed by plants in photosynthesis, transferred through food chains, released back by respiration and decomposition. Maintains atmospheric CO2 balance.
10. What are the causes and prevention of air pollution?
Answer: Causes: vehicle emissions, burning fuels, industrial waste. Prevention: afforestation, use of public transport, filters in factories.
1. Find the derivative of sin(x²) with respect to x.
Answer: Let y = sin(x²).
Then dy/dx = cos(x²) × 2x = 2x cos(x²).
2. Evaluate ∫ (2x + 3) dx.
Answer: ∫ (2x + 3) dx = x² + 3x + C.
3. Find the coordinates of the point where the line y = 2x + 3 intersects the line y = -x + 1.
Answer: At intersection, 2x + 3 = -x + 1 → 3x = -2 → x = -2/3.
Then y = 2(-2/3) + 3 = 5/3.
Point = (-2/3, 5/3).
4. Solve the matrix equation: A = [[2, 1], [3, 2]], find A⁻¹.
Answer: |A| = (2×2) - (3×1) = 1.
Adj(A) = [[2, -1], [-3, 2]].
Hence, A⁻¹ = Adj(A)/|A| = [[2, -1], [-3, 2]].
5. Find the mean and standard deviation of 2, 4, 6, 8.
Answer: Mean = (2 + 4 + 6 + 8)/4 = 5.
Deviation = (-3, -1, 1, 3).
Variance = (9 + 1 + 1 + 9)/4 = 5.
Standard deviation = √5 ≈ 2.24.
Q1. What is the principle behind a cyclotron?
Q2. Explain how semiconductor diodes work as rectifiers.
Q3. Write the difference between primary and secondary batteries.
Q4. Explain Le Chatelier’s principle with examples.
Q5. Write two differences between physisorption and chemisorption.
Q6. Explain the role of DNA polymerase in DNA replication.
Q7. What is the difference between endocrine and exocrine glands?
Q8. State two uses of polymers in everyday life.
Q9. Evaluate ∫ (x² + 1/x) dx.
Q10. Find the slope of the tangent to the curve y = x² + 3x at x = 2.
Using Class 12 important questions in the right way can upgrade your preparation from “I have read everything” to “I can actually solve exam-style problems confidently.” Here’s how to get the maximum benefit:
Before solving, check which part of the chapter the question comes from. This helps you identify:
This habit builds strong conceptual clarity , which is essential for Class 12 Board-level answers.
Start with simple, direct ones, then gradually move to analytical and long-form questions.
This helps you:
When answering, follow the CBSE pattern:
Practise writing full answers so your hand-speed, structure, and clarity improve together.
Even if you understand the concepts, Class 12 papers are lengthy. Timing practice helps you:
After solving, compare your solutions to marking scheme style answers:
Here are some of the benefits that can help you:
Q1. Are Class 12 important questions enough for Board exam preparation?
Ans. They cover the most important and frequently tested concepts, but you should combine them with NCERT reading and sample paper practice for full preparation.
Q2. How many times should I practise these important questions?
Ans. Here are some of the following times you should practise these important question:
Q3. Do important questions include CBSE’s latest case-based and competency-based questions?
Ans. Yes, high-quality important question sets include case-based, assertion–reason, and application-based problems aligned with the latest exam trends.
Q4. Should I focus only on important questions or solve full papers too?
Ans. Important questions strengthen concepts. Full papers improve time management and exam stamina. You need both for a strong board exam performance.
Q5. How do I know if I’m writing answers in the correct CBSE format?
Ans. Cross-check with:
Q6. What should I do if I get many important questions wrong?
Ans. Don’t memorise the solutions, Instead:
This is the fastest way to fix conceptual gaps.
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