CBSE Class 10 Science Sample Paper 2026–27: Chemistry MCQs Q17–24 Explained
Attempt Chemistry questions Q17–24 in the official Science sample paper, then use this 13:00 walkthrough to review the reasoning. Choose a chapter below.
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What this episode covers
The eight Chemistry objective questions Q17–24 in Section B. This includes the assertion–reason item Q24. Biology, Physics and longer Chemistry answers are outside this episode.
These are original TutorMax explanations of the official paper, not an official CBSE video. Narration uses text-to-speech. The readable notes summarise the reasoning; they are not a verbatim transcript. Use the official marking scheme when reviewing your paper.
Keep the reasoning, not just the answer letter
Attempt the official question before watching its explanation. Afterwards, close the answer and explain the key idea in your own words. If you can only remember the letter, revisit the relevant note.
Q17 · Colour change and substance change
A colour change alone does not establish a chemical reaction. In the stated crystal-spacing mechanism, the arrangement changes without a new substance being described.
Revisit this explanation on YouTube ↗Q18 · Chlor-alkali products
Chlorine forms at the anode, hydrogen at the cathode, and sodium hydroxide is in solution near the cathode. In a matching table, check the product, location and use: one correct column cannot rescue an incorrect row.
Revisit this explanation on YouTube ↗Q19 · Hard water and soap
Calcium and magnesium ions form insoluble salts with soap: the visible scum uses up some soap. Do not blame sodium ions or confuse scum with lather.
Revisit this explanation on YouTube ↗Q20 · Water of crystallisation
Water of crystallisation is included in a fixed ratio in the crystal structure. Plaster of Paris has one H₂O per two CaSO₄ units; washing soda has ten waters and gypsum two. Baking soda has no water of crystallisation. Hydrogen and oxygen in a formula are not enough to establish a hydrate.
Revisit this explanation on YouTube ↗Q21 · Structural isomers
Check the molecular formula first, then compare atom connectivity. Different drawings are not necessarily different structures; compounds with different formulae cannot be structural isomers.
Revisit this explanation on YouTube ↗Q22 · Nitrogen in a food packet
Nitrogen flushing reduces oxygen exposure and slows oxidation and rancidity. This is a different explanation from claiming that every preservative works as an antioxidant.
Revisit this explanation on YouTube ↗Q23 · Aluminium's protective surface
An adherent aluminium oxide layer slows further corrosion under ordinary conditions. A reactive metal can develop a protective surface; protection does not mean it can never corrode.
Revisit this explanation on YouTube ↗Q24 · Official key and interpretation caveat
CBSE's marking scheme gives B: both statements are true, but the reason is not the correct explanation. Some independent solutions choose A. Follow the official key for this paper while keeping the observations separate from the wording dispute: naming onion as an olfactory indicator does not specify which medium removes or retains its odour.
Revisit this explanation on YouTube ↗Can you use the idea in a changed example?
These questions are original TutorMax practice, not official CBSE questions. Try them without the video or notes. They check a few ideas from this episode, not whole-subject readiness.
Fresh practice 1
Two compounds have formula C₄H₁₀ but different carbon connections. What two facts let you call them structural isomers?
Check the reasoning
Their molecular formulae are identical and their atom connectivity differs. The same atoms drawn in a different orientation would not be enough. Revisit Q21 if you only compared the appearance of the drawings.
Fresh practice 2
A salt has hydrogen and oxygen in its formula. Does that alone prove water of crystallisation? Explain.
Check the reasoning
No. Water of crystallisation is water included in a fixed ratio in the crystal structure, not simply hydrogen and oxygen atoms somewhere in the compound. Revisit Q20 and distinguish a hydrate formula from baking soda.
Choose your next step
If an idea was unclear, revisit the concept guide. If the idea makes sense but you misread the options, return to that video chapter and explain why the tempting choice fails. Then use the paper-review guide to plan your next attempt.
Video and authored source package checked 6 October 2026.