Class 10 Science Chapter Weightage 2026-27: Unit Marks and the 5 Chapters That Carry 40%

Last updated: 23 September 2026

What is the unit-wise weightage for Class 10 Science?

Every year students ask which chapters to revise first, and every year the honest answer is the same: look at the marks, not at the number of pages. Here is the official unit-wise distribution for the 2026-27 session.

Which five chapters carry the most marks?

Marks are not spread evenly inside a unit. Across recent question papers and sample papers, five chapters do most of the work:

• Carbon and its Compounds — the single heaviest chemistry chapter, and the one that reliably brings long-answer questions on nomenclature, homologous series and reactions.
• Life Processes — the heaviest biology chapter, with diagram-based questions that carry marks for labelling alone.
• Heredity — small chapter, high return. Monohybrid and dihybrid crosses are predictable and scoring.
• Light — Reflection and Refraction — ray diagrams, mirror and lens formulae, numericals. The most practised chapter in physics for good reason.
• Electricity — circuit questions and numericals on Ohm’s law, resistance in series and parallel, and heating effect.

Together these five sit near 40% of the theory paper. That does not mean the rest can be skipped — it means that if your revision time is limited, this is where the first hours belong.

Why does weightage matter more than the number of chapters?

There are thirteen chapters in the Class 10 Science book. Most students revise them in book order, giving each roughly the same time. The paper does not work that way: Our Environment carries five marks and Life Processes carries several times that. Revising both for an hour each is not fair to your marks.

The fix is not to work more hours. It is to sort the chapters by marks, then by how confident you are, and start where those two lists disagree most — a heavy chapter you are weak in.

Where do students actually lose marks in the heavy chapters?

None of those are knowledge problems. They are habit problems, and they are the cheapest marks to recover in the last three weeks.

How should you use this chart in the last three weeks?

1. Rank, don’t read. Write the five heavy chapters on one side of a page and mark yourself out of ten on each.
2. Start where the gap is widest — high marks, low confidence.
3. Twenty minutes per chapter, not two hours. Write what you remember first, then open the book and correct yourself. Recall before re-reading is what makes it stick.
4. Ten questions after each chapter. If you cannot answer them, the chapter is not done — however long you spent on it.
5. Leave the last three days for revision only. No new chapters.

What about the 20 internal assessment marks?

Internal assessment is made up of periodic tests, the practical work and portfolio, and subject enrichment. These marks are awarded by your school through the year, and they are usually the easiest twenty marks on the paper to protect — provided the practical file is complete and submitted on time. Students who chase theory and neglect the file give away marks nobody can recover later.

Frequently asked questions

Is the Class 10 Science paper 80 marks or 100 marks?
The theory paper is 80 marks. Internal assessment adds 20, for a total of 100.

Which is the highest-weightage unit in Class 10 Science?
Units I (Chemical Substances) and II (World of Living) are joint highest at 25 marks each — half the theory paper between them.

How many chapters are there in Class 10 Science?
Thirteen, following the rationalised NCERT syllabus, grouped into the five units above.

Is chapter-wise weightage officially published by CBSE?
CBSE publishes unit-wise weightage in the curriculum document. Chapter-level weightage is an estimate based on the sample papers and previous years’ question papers, so treat it as a guide to priority, not a guarantee.

Which chapters should I revise first if I have only one week?
Carbon and its Compounds, Life Processes, Electricity, Light and Heredity. They carry the most marks and reward focused revision.

Does this weightage apply to the 2027 board exam too?
The unit structure has been stable for several sessions. Always check the current CBSE curriculum document for your year before building a final plan.