Tamil Nadu HSC Class 12 Science Important Questions 2027 - Physics Chemistry Biology

In short: Tamil Nadu HSC Class 12 science theory exams run from March 3 to March 29, 2027. Each science subject carries 70 marks for theory with four sections of increasing mark value. Part IV questions (5-mark and 10-mark) alone carry 35 to 40 percent of total marks. This guide targets the most expected Part III and Part IV questions for Physics, Chemistry, Bio-Botany, and Bio-Zoology based on Samacheer Kalvi patterns.

TN HSC Science Exam Structure

Part IV carries 25 to 30 marks (5 questions × 5 marks each). Combined with Part III (3-mark questions), the long-answer sections determine your grade. MCQs are important but the real scoring happens in Parts III and IV.

Physics Important Questions (70 marks theory)

Electrostatics (8-10 marks)

• Derive Coulomb's law in vector form. Explain the principle of superposition. (5 marks)
• Derive the expression for electric potential at a point due to a point charge. (5 marks)
• Define electric flux. State and prove Gauss's theorem. Apply it to find the field due to an infinite charged plane. (5 marks)
• Derive the expression for the capacitance of a parallel plate capacitor. How does inserting a dielectric affect it? (5 marks)

Current Electricity (6-8 marks)

• State and explain Kirchhoff's rules. Solve the given circuit to find current in each branch. (5 marks)
• Derive the expression for the balancing condition of a Wheatstone bridge. (3 marks)
• Explain the principle and working of a potentiometer. How is it used to compare EMFs? (5 marks)

Magnetism and Electromagnetic Induction (8-10 marks)

• Derive the expression for the torque on a current loop in a uniform magnetic field. (5 marks)
• State Faraday's laws of electromagnetic induction. Derive the expression for the EMF induced in a rotating coil. (5 marks)
• Explain the construction and working of a transformer. Why is the core laminated? (5 marks)

Optics (10-12 marks)

• Derive the lens maker's formula. (5 marks)
• Explain Young's double slit experiment. Derive the expression for fringe width. What happens when white light is used? (5 marks)
• State Huygens' principle. Using it, derive Snell's law of refraction. (5 marks)
• What is polarisation? Explain polarisation by reflection and state Brewster's law. (3 marks)

Modern Physics and Semiconductor (8-10 marks)

• State the laws of photoelectric emission. Derive Einstein's photoelectric equation. Explain threshold frequency. (5 marks)
• Derive the expression for the radius of the nth Bohr orbit in a hydrogen atom. (5 marks)
• Explain the working of a p-n junction diode as a half-wave rectifier. Draw input and output waveforms. (5 marks)
• Explain the working of a transistor as a common-emitter amplifier. (5 marks)

For chapter-wise weightage, see TN HSC Class 12 Science marks distribution and the TN HSC Maths weightage guide.

Chemistry Important Questions (70 marks theory)

Physical Chemistry (20-22 marks)

• State and explain Raoult's law. What are ideal and non-ideal solutions? Draw vapour pressure diagrams for positive and negative deviations. (5 marks)
• Derive the integrated rate law for first-order reactions. How is the rate constant determined from a graph? (5 marks)
• State Faraday's laws of electrolysis. Calculate the mass of copper deposited when a current of 3A passes for 1 hour. (5 marks)
• Define molar conductivity. How does it vary with dilution for strong and weak electrolytes? Draw graphs and explain. (5 marks)

Inorganic Chemistry (12-15 marks)

• What are coordination compounds? Explain Werner's theory with examples. Write IUPAC names of given complexes. (5 marks)
• Explain crystal field theory for octahedral complexes. What is crystal field splitting energy? (5 marks)
• What are lanthanoids and actinoids? Explain lanthanoid contraction and its consequences. (3 marks)
• How is copper extracted from its ore? Describe the steps from concentration to refining. (5 marks)

Organic Chemistry (22-25 marks)

• Explain the SN1 and SN2 mechanisms with examples. How do they differ in stereochemistry? (5 marks)
• Describe the methods of preparation of phenol. Explain why phenol is more acidic than ethanol. (5 marks)
• What is aldol condensation? Explain the mechanism with an example. What is Cannizzaro reaction? (5 marks)
• Explain Hofmann bromamide degradation. Write the product when given amide is treated with Br2/NaOH. (3 marks)
• Classify amino acids. What is the zwitter-ionic form? Explain the primary structure and secondary structure of proteins. (5 marks)
• What are nucleic acids? Explain the double helical structure of DNA with a diagram. Differentiate between DNA and RNA. (5 marks)
• Describe addition and condensation polymerisation with two examples each. What is the difference between thermoplastics and thermosetting plastics? (5 marks)

Bio-Botany Important Questions (70 marks theory)

Plant Anatomy and Physiology (15-18 marks)

• Describe the internal structure of a dicot root with a labelled diagram. Compare with a monocot root. (5 marks)
• Explain the C3 cycle (Calvin cycle) of photosynthesis with a diagram. Where does it occur? (5 marks)
• What is transpiration? Explain the mechanism of stomatal transpiration. What factors affect the rate? (5 marks)
• Describe the process of biological nitrogen fixation. What role do Rhizobium bacteria play? (5 marks)

Reproduction in Plants (12-14 marks)

• Describe the process of microsporogenesis. Draw a labelled diagram of a mature pollen grain. (5 marks)
• Describe the structure of a mature embryo sac (megagametophyte). Explain double fertilisation and triple fusion. (5 marks)
• What is polyembryony? Give examples. Explain apomixis and its types. (3 marks)

Genetics and Biotechnology (15-18 marks)

• Explain Mendel's law of independent assortment using a dihybrid cross. Show the 9:3:3:1 ratio with a Punnett square. (5 marks)
• Describe the structure of DNA as proposed by Watson and Crick. What is Chargaff's rule? (5 marks)
• Explain the process of transcription in eukaryotes. What is split gene concept? (5 marks)
• Describe the steps involved in recombinant DNA technology. What is a cloning vector? (5 marks)

Plant Ecology (8-10 marks)

• Describe the structure of an ecosystem. Explain energy flow with a diagram. What is the 10% law? (5 marks)
• What is ecological succession? Compare primary and secondary succession. (5 marks)

Bio-Zoology Important Questions (70 marks theory)

Human Physiology (15-18 marks)

• Describe the mechanism of breathing in humans. Explain the role of the diaphragm and intercostal muscles. Draw a labelled diagram. (5 marks)
• Explain the structure of the human kidney. Draw a labelled diagram of a nephron. Describe the process of urine formation. (5 marks)
• Describe the cardiac cycle. What are systole and diastole? Draw a labelled diagram of the human heart. (5 marks)

Reproduction and Genetics (15-18 marks)

• Describe the human female reproductive system with a labelled diagram. Explain the menstrual cycle. (5 marks)
• Explain the Hershey-Chase experiment. How did it prove that DNA is the genetic material? (5 marks)
• Explain the lac operon model of gene regulation with a diagram. (5 marks)
• What are sex-linked disorders? Explain colour blindness and haemophilia with pedigree charts. (5 marks)

Evolution and Biology in Human Welfare (10-12 marks)

• What are the evidences of organic evolution? Explain homologous and analogous organs with examples. (5 marks)
• Describe the life cycle of Plasmodium (malaria parasite). How is malaria transmitted and controlled? (5 marks)

Biotechnology and Immunology (8-10 marks)

• What are transgenic animals? Give examples and applications. (3 marks)
• Explain the structure and function of antibodies. What are the types of immunity? (5 marks)

Priority Chapters for Maximum Marks

Study Strategy for Last 30 Days

For complete preparation strategy, see our TN Board JEE NEET bridge guide and study smart tips.

Frequently Asked Questions

Are TN HSC Science questions predictable?

Yes, to a significant extent. The Samacheer Kalvi textbook is the sole source. Part IV questions often repeat the same concepts with minor variations. Book-back exercises cover most of what appears.

How much do practicals matter?

Practical exams carry 20 marks and are held in February before theory exams. These are relatively easier to score. Prepare the standard experiments and viva questions from your textbook.

Should I focus more on Part IV or Part I MCQs?

Both matter, but Part IV has a higher marks-to-questions ratio. One 5-mark answer written well equals five MCQs. If time is limited, prioritise Part IV preparation.

Is the TN HSC Science syllabus different from NCERT?

The Samacheer Kalvi syllabus overlaps significantly with NCERT but has some unique topics and a different chapter sequence. Stick to your Samacheer Kalvi textbook for board exams. Use NCERT additionally only if preparing for NEET or JEE.

How do I write 5-mark answers effectively?

Use the answer writing tips for board exams. Include diagrams, label clearly, write step-by-step, and conclude with a summary sentence.

What if I cannot finish the paper in time?

Practice time management: allocate roughly 1 minute per mark. For a 70-mark, 3-hour paper, you have about 2.5 minutes per mark. Start with questions you are most confident about.

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