Where the marks go in CBSE Class 10 Science

In CBSE Class 10 Science, marks are lost where the marking scheme splits an answer into small parts. The 2026 scheme gives half marks for a formula, a working line, an answer with its unit, and each label on a diagram. An answer that skips one part loses that half mark, even when the science is right.

How is the CBSE Class 10 Science paper divided?

Into three sections: Biology, then Chemistry, then Physics. CBSE's Science sample paper for 2026-27 has 39 questions for 80 marks in 3 hours. Biology is questions 1 to 16 and carries 30 marks. The other 20 marks of the subject come from the school, through internal assessment.

For the 2026 exam, CBSE also split the Science answer book into the same three sections. Its circular of 9 December 2025 says an answer written in the wrong section "will not be evaluated". Check your year's instructions. What a pre-board is for explains why CBSE asked schools to practise this.

The Science syllabus for 2026-27 gives the weight of each unit. Chemical substances carry 25 marks. The world of living carries 25. Light carries 12 and electricity 13, so 25 marks of physics. Natural resources carry 5.

Each section loses marks in its own way. A physics numerical loses them in the working. A chemistry answer loses them in the equation. A biology answer loses them in the diagram and the number of points given.

Where are marks lost in CBSE Class 10 Science?

In the half marks. CBSE publishes the marking schemes for its board papers after the exam. The 2026 Science scheme marks answers in value points, down to half a mark. Here is one 2-mark numerical from set 31/1/1, question 34(b).

An electric heater is rated 220 V and 11 A. Find the power it uses at 200 V. The scheme gives half a mark for each of four lines. The first is the formula for resistance, R = V/I. The second is the working, which gives R = 20 Ω. The third is the formula for power, P = V²/R. The fourth is the answer, printed as 2000 W or 2 kW.

A student who writes only "2000 W" shows one of the four lines. The other three have nothing on the page to be marked against. That is why students lose marks they actually knew, and how step marking splits an answer explains the rule behind it.

Are marks cut for not writing units?

The scheme prints the final answer with its SI unit: "2000 W / 2 kW". So the last half mark is for the answer with its unit. The scheme for that set prints no separate rule about a missing unit. We will not invent one.

CBSE's Assessment and Evaluation handbook does say one thing. Method marks are not lost for an error in units. That protects the formula and working lines. It says nothing that protects the answer line. The safe habit is to write the unit every time.

Do diagrams carry marks in CBSE Science?

Yes, and the labels carry their own. In set 31/1/1, question 12 asks for a diagram of a pollen grain growing on the flower, with two parts named. The scheme gives 1 mark for the diagram. It gives half a mark for labelling the stigma and half for the pollen tube.

Ray diagrams have a rule of their own. Question 35 is on a defect of the eye. There, the scheme takes off half a mark for not showing the direction of the ray. The ray can be in the right place and still lose half a mark without its arrow.

Are marks cut for an unbalanced chemical equation?

In the 2026 scheme, yes, where it says so. Question 27(b) of set 31/1/1 asks for three balanced equations. The scheme says to deduct half a mark for an equation that is not balanced, or balanced wrongly. It is not every question: in the same set, question 28(b) prints "balancing is optional".

The balanced equation can also carry a whole answer. In set 31/1/3, question 26 asks what is seen in three reactions. The scheme gives full marks even if only the balanced equations are written.

Does the answer have to match the marking scheme word for word?

No. The instructions printed at the top of the scheme say its value points are guidelines, not the complete answer. A student may use their own words, and a correct point earns its mark. What a marking scheme contains shows how value points are laid out. How an examiner marks one real answer follows one from start to finish.

For the two competency-based questions in a Class 10 paper, the instructions go further. If the answer shows the right skill but is not in the scheme, the marks are still due. Case-based and competency questions, explained shows how those questions are built.

One more instruction helps a student who slips. An error is cut only once, not again for its effect on later steps.

How should you write a Class 10 Science answer?

• Write a numerical in three kinds of line. The formula, the numbers put in, then the answer with its unit. Each can be a half mark of its own.
• Label every part the question names. In question 12, the labels were worth as much as the drawing.
• Put the arrows on every ray. The 2026 scheme takes half a mark off a ray diagram without them.
• Balance each equation before moving on. The 2026 scheme takes half a mark off an unbalanced equation in question 27(b).
• Give as many points as the question asks for. A 2-mark question that asks for two points has a mark on each. How to write answers to get full marks shows answer length for each question size.

The same habits apply to ICSE. How marks work in ICSE Physics numericals covers units there. To plan the last month around these habits, see turning a mark-loss report into a 30-day plan. The 2026 board season, paper by paper sets the Science paper beside the others.

About the author

Deepti Sardana

Founder Member & Academic Lead

An IIT alumna (M.Sc., M.Phil.) with over 25 years in teaching, child psychology and learning assessment. As Academic Lead at EduBrahma, she leads the method TRUtesting uses to find where and why a child loses marks.

Deepti Sardana on LinkedIn