Reference: This post is based on the CISCE document Analysis of Pupil Performance – ICSE Chemistry (Science Paper-2), 2025, published by the Research Development and Curriculum Division, CISCE, New Delhi, in October 2025.
Every year, CISCE examiners go through lakhs of answer scripts and record where students lose marks. Their 2025 report for ICSE Chemistry is one of the most useful study tools a Class 10 student can read, and I've summarised it below.
2,25,668candidates appeared
60.5average marks out of 100
70.9top state average (Goa)
The main finding: most marks were lost to careless reading, incomplete observations and imprecise writing, not to a lack of knowledge.
ICSE Chemistry Answer-Writing Tips to Score Full Marks
- Read every key word. Many students missed the word not in Q1 (xiii) and excess in Q8 (iii). Underline bold and italic words before you answer.
- Answer exactly what is asked. If a question asks for a name, write the name; if it asks for a formula, write the formula. When told "do not identify", use the given letters (MP2, not MgCl2).
- Write complete observations. State the colour, the state and what happens in excess, e.g. "white precipitate, soluble in excess NH4OH". Write "reddish-brown gas", not just "brown gas" or "NO2 is formed".
- Show all steps in numericals. Balanced equation → molar mass → ratio → substitution → answer with units. Students who gave only the final answer (98 g, 6) lost marks.
- Balance equations and include all products. Use the simplest ratio (2H+ + 2e− → H2) and write conditions over the arrow.
- Use exact definitions and notation. Avogadro's Law needs "under the same conditions of temperature and pressure". Write the period as 3, not III; write valency with its sign (−3); write the metal first in a formula.
- Draw dot-and-cross diagrams correctly. Use dots for one element and crosses for the other, show charges on ions and include lone pairs.
- Recheck before you submit. The examiners specifically listed calculation slips as a cause of lost marks.
Quick check: Before moving to the next question, ask yourself: "Did I answer what was asked, in the form it was asked?"
Most Confusing Concepts in ICSE Chemistry
Most wrong answers came from mixing up two similar-looking ideas. Here are the mix-ups the examiners saw most often:
| Common confusion | Correct concept |
|---|---|
| Drying agent vs dehydrating agent | A drying agent removes moisture (CaO dries NH3). A dehydrating agent removes the elements of water from a compound. |
| Smallest atom = best reducing agent | It's the opposite: the largest atom in a group loses electrons most easily, so it is the best reducing agent. |
| Oxidising vs reducing agent | Define them by electron transfer. In S + 2H2SO4 → 3SO2 + 2H2O, H2SO4 is the oxidising agent. |
| CuSO4 electrolysis with copper electrodes | The anode dissolves and the Cu2+ concentration stays unchanged. |
| Conc. vs dilute HNO3 with copper | Concentrated acid gives reddish-brown NO2; dilute acid gives colourless NO. |
| Valency vs valence electrons | A Group VA element has 5 valence electrons but a valency of −3. |
| Roasting vs calcination | Roasting heats sulphide ores in air. Calcination heats carbonate ores in the absence of air. |
| Baeyer's vs Hall–Héroult process | Baeyer's process concentrates bauxite; the Hall–Héroult process extracts aluminium. |
| IUPAC longest chain | Choose the longest chain that contains the double bond: pent-2-ene, not 1-methylbut-1-ene. |
| Salt preparation method | Insoluble salts (PbCl2, PbSO4) are made by precipitation, FeCl3 by direct combination and Na2SO4 by titration. |
| Gay-Lussac's Law | It applies to gases only. Liquid water has no volume in the answer. |
| Vapour density | Molecular mass = 2 × vapour density. |
Important Topics for the ICSE Chemistry Board Exam
These topics appeared again and again in the 2025 paper, and the examiners flagged them as difficult:
- Mole concept and stoichiometry: vapour density, Gay-Lussac's Law, volumes at STP, empirical and molecular formula.
- Organic chemistry: IUPAC names, structural formulas, isomers, general formulas.
- Analytical chemistry: precipitates with NaOH and NH4OH, gas tests, distinguishing between pairs of compounds.
- Electrolysis: electrode reactions, active vs inert electrodes.
- Chemical bonding: ionic, covalent and coordinate dot-and-cross structures.
- Periodic table: trends in ionisation potential, reducing power and valency.
- Sulphuric acid, nitric acid and ammonia: preparation, properties, industrial processes and catalysts.
- Metallurgy and salts: ore concentration, Baeyer's process, methods of salt preparation.
Also practise assertion–reason and application-based questions. The examiners named both as weak areas.
What ICSE Chemistry Teachers Should Focus On
- Lab demonstrations: SO2 with KMnO4, copper with conc. and dilute HNO3, and electrolysis of CuSO4 and acidulated water.
- Observation drills: add a little → observe → add in excess → observe. Teach students to keep observation separate from inference.
- Wall charts of gas tests and solubility rules that students can refer to all the time.
- Daily practice in equations and numericals: stepwise working, units, and a balanced equation first.
- Organic chemistry: general formulas, choosing the longest chain, the lowest locant for the functional group, and tetravalency.
- Bonding worksheets, including coordinate bonds (NH4+, H3O+) drawn with an arrow.
- Exam technique: regular assertion–reason practice and error-spotting worksheets.
Key Takeaway
Precision wins marks. Read carefully, write complete observations, show every step and use exact terms. Fix these habits now and you can gain easy marks in your ICSE 2026 Chemistry paper.
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