CBSE Class 12 science subjects don't share one pattern — and that trips up most students. Physics, Chemistry and Biology are 70 theory + 30 practical; Maths is 80 theory + 20 internal assessment. Every subject totals 100. That difference matters more than any chapter list: in Maths your practical marks don't exist, and in Physics 30 marks are decided before you enter the exam hall. For exact unit-wise marks, read your own syllabus PDF at cbseacademic.nic.in — this page shows you exactly how, in about five minutes, because those numbers are revised and every blog quoting them (including this one) would eventually be wrong.
The pattern: three splits, not one
Students talk about "the Class 12 pattern" as if there's one. There isn't — and knowing which one applies to you changes where your marks come from:
So a PCM student is sitting three different arrangements at once: 70+30 in Physics and Chemistry, 80+20 in Maths. A PCB student has three 70+30 subjects and no 80+20 science at all. Your revision plan should not treat them identically.
Why the split matters more than the chapter list
Most students hunt for chapter weightage and never look at this. That's backwards, and here's the arithmetic:
In Physics, 30 of your 100 marks are practical — experiment, viva, file, project. Those are scored in your school, over the year, in conditions where you can prepare completely and nobody is testing you under a three-hour clock. They are, mark for mark, the easiest 30 marks in the subject — and the ones students most often treat casually because "the real exam is in March".
Now do the sum: a student who loses 8 practical marks in Physics has to make them up from a 70-mark theory paper, where marks are far harder to win. Chapter weightage tells you where to spend your revision hours. The split tells you where your marks actually are. The second question is bigger, and almost nobody asks it.
The unit structure of each subject
Here's what each subject is actually made of. Unit names and structure are stable; the exact marks per unit are what you'll pull from the PDF in the next section.
Physics — 70 marks theory, 9 chapters in 5 units
| Unit | Chapters |
|---|---|
| Electrostatics & Current Electricity | Electric Charges and Fields; Electrostatic Potential and Capacitance; Current Electricity |
| Magnetic Effects & Magnetism; EMI & AC | Moving Charges and Magnetism; Magnetism and Matter; Electromagnetic Induction; Alternating Current |
| Electromagnetic Waves & Optics | Electromagnetic Waves; Ray Optics and Optical Instruments; Wave Optics |
| Dual Nature; Atoms & Nuclei | Dual Nature of Radiation and Matter; Atoms; Nuclei |
| Electronic Devices | Semiconductor Electronics |
Electrostatics + Current Electricity and the Magnetism/EMI/AC block are consistently the two heaviest units — that much is stable year to year.
Chemistry — 70 marks theory, three branches
| Branch | Chapters |
|---|---|
| Physical | Solutions; Electrochemistry; Chemical Kinetics |
| Inorganic | d- and f-Block Elements; Coordination Compounds |
| Organic | Haloalkanes and Haloarenes; Alcohols, Phenols and Ethers; Aldehydes, Ketones and Carboxylic Acids; Amines; Biomolecules |
Organic carries the most chapters. Electrochemistry, Coordination Compounds and Aldehydes/Ketones/Carboxylic Acids are reliably among the higher-mark chapters.
Mathematics — 80 marks theory, 13 chapters in 6 units
| Unit | Chapters |
|---|---|
| Relations & Functions | Relations and Functions; Inverse Trigonometric Functions |
| Algebra | Matrices; Determinants |
| Calculus | Continuity and Differentiability; Applications of Derivatives; Integrals; Applications of the Integrals; Differential Equations |
| Vectors & 3D Geometry | Vectors; Three-dimensional Geometry |
| Linear Programming | Linear Programming |
| Probability | Probability |
Calculus is the largest unit by a wide margin — five of the thirteen chapters. If you revise by unit rather than by chapter, this is the one that pays.
Biology — 70 marks theory, 13 chapters in 5 units
| Unit | Chapters |
|---|---|
| Reproduction | Sexual Reproduction in Flowering Plants; Human Reproduction; Reproductive Health |
| Genetics & Evolution | Principles of Inheritance and Variation; Molecular Basis of Inheritance; Evolution |
| Biology & Human Welfare | Human Health and Disease; Microbes in Human Welfare |
| Biotechnology | Biotechnology: Principles and Processes; Biotechnology and its Applications |
| Ecology | Organisms and Populations; Ecosystem; Biodiversity and Conservation |
Genetics & Evolution and Ecology are consistently the heavier units.
How to read your own weightage in 5 minutes
This is the most useful thing on this page, and it takes less time than reading a blog's version of the table:
| Step | Do this |
|---|---|
| 1 | Go to cbseacademic.nic.in — the official academic site (not the main cbse.gov.in) |
| 2 | Find Curriculum → the current session → Senior Secondary (XI–XII) |
| 3 | Open your subject's PDF. Every science subject's curriculum begins with a unit-wise marks table — usually on page 1 or 2. |
| 4 | Photograph that table. That's your weightage — official, current, and specific to your session. |
| 5 | Scroll to the end for the practical/internal breakdown and the deleted topics list. Both matter as much as the marks table. |
The question types — and the one most students misjudge
Board papers mix objective questions, short answers of a couple of lengths, long answers, and case/source-based questions. The exact counts shift between sessions, so pull them from the current sample paper at cbseacademic.nic.in rather than from any blog.
But one thing is stable and worth knowing: case-based questions are where prepared students lose marks unexpectedly. They look like comprehension, so students relax — but they're testing whether you can apply a concept to an unfamiliar situation, which is a different skill from reproducing it. You can't revise for them by reading; you revise for them by solving unfamiliar problems.
The deleted-topics trap
The syllabus has been rationalized — topics and whole chapters have been removed. This creates a specific, avoidable waste:
| The trap | What happens |
|---|---|
| Old previous-year papers | Contain questions on deleted topics. Students panic over a question that can no longer be asked. |
| Old reference books | Cover deleted chapters at full length. Weeks spent on content worth zero marks. |
| Senior siblings' notes | Written against a different syllabus |
| Blogs and videos | Rarely updated after rationalization; the deletions are the first thing to go stale |
The fix is the same five-minute method: the deleted topics list is in the official syllabus PDF, at the end. Read it once, mark those pages in your book, and never think about them again. Students routinely lose weeks to this.
How to actually use weightage
Knowing a unit carries more marks is only useful if it changes what you do. Four ways it should:
| Use it to… | Not to… |
|---|---|
| Order your revision — heaviest units first, and revisited most often | Skip light units. Every chapter is examinable, and small units ask the easiest questions. |
| Allocate your weakest hours — if Calculus is your worst and it's the biggest unit, that's your answer | Assume heavy = hard. Calculus is heavy; Linear Programming is one procedure. |
| Decide what gets a third revision when time is short | Build a plan that only covers the top half of the syllabus |
| Sanity-check your practical prep against 30 marks (science) | Forget that 30 marks aren't in the theory paper at all |
Revise the heavy units from topper handwritten notes
Once you know which units carry your marks, the next question is what you revise from:
- Class 12 Physics, Chemistry, Maths & Biology — full syllabus, NCERT-aligned, current rationalized content
- Colour-coded with formula boxes and diagrams — short enough to revise a unit in one sitting
- Real handwritten notes by toppers — IITians, NITians and district toppers
- Instant PDF or printed book (COD available, all-India delivery) · English & Hindi medium
FAQs
What is the CBSE Class 12 exam pattern for science subjects?
Physics, Chemistry and Biology are 70 marks theory plus 30 marks practical, while Mathematics is 80 marks theory plus 20 marks internal assessment. Every subject totals 100, but the splits are different — which changes where your marks come from.
Where can I find the official CBSE Class 12 chapter weightage?
In your subject's curriculum PDF at cbseacademic.nic.in, under Curriculum for the current session, Senior Secondary. Every science subject's document opens with a unit-wise marks table, usually within the first two pages.
Why do weightage tables on different websites disagree?
Because CBSE revises unit marks between sessions and most articles copy each other rather than the source, so stale tables spread. The official syllabus PDF is current by definition and specific to your session.
Which unit has the highest weightage in Class 12 Maths?
Calculus, by a wide margin — it contains five of the thirteen chapters, covering Continuity and Differentiability, Applications of Derivatives, Integrals, Applications of the Integrals and Differential Equations.
How many marks is the practical exam in Class 12 Physics?
30 of the 100 marks, covering the experiment, viva, practical file and project. They're assessed in your school across the year, which makes them the easiest marks in the subject — and the ones most often treated casually.
Should I skip low-weightage chapters in Class 12?
No. Low-weightage chapters usually ask the simplest questions in the paper — pure recall with no application — so skipping them trades easy marks for hard ones. Use weightage to decide what to revise first and most, never what to skip.
How do I know which topics have been deleted from the syllabus?
The deleted topics list is at the end of your subject's official syllabus PDF. Read it once and mark those pages in your book — students routinely lose weeks revising content that can no longer be asked.
What are case-based questions in CBSE Class 12?
Questions that present an unfamiliar situation and ask you to apply a concept to it. They look like comprehension so students relax, but they test application rather than recall — you prepare for them by solving unfamiliar problems, not by reading.