Assertion (A): Tooth decay begins when the pH of the mouth falls below 5.5. Reason (R): Bacteria in the mouth produce acids by the degradation of sugar and food particles. Choose the correct option.

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is not the correct explanation of A

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CBSE Class 10 Science Board Paper — MCQs with Answers

Original paper · CBSE patternWritten by our subject team, not a reprint of an official sample paper.

Questions: 30
Time: 60 min
Marking: +1, no negative marking
Mix: 15 Easy · 16 Medium

Board Paper — CBSE Class 10 Science is a full 30-question objective paper for Class 10 Science, written in the CBSE board pattern and marked the way the board marks: +1 for a correct answer and 0 for a wrong one — no negative marking, exactly like the real board paper. It draws 30 objective questions from a 31-question pool spanning the whole Class 10 Science syllabus, so a retake is a genuinely different paper rather than the same questions again.

Difficulty is 15 Easy · 16 Medium, weighted the way the board weights Section A. You get 60 minutes — about 120 seconds a question, the pace the real paper demands. 6 of the questions are solved in full below, with the correct option and a worked explanation for each; the remaining 24 are timed and scored when you sign in free.

From 2026-27 CBSE Class 10 has two board exams a year: the first around 15 February – 10 March 2027 is compulsory, and an optional improvement exam in May 2027 lets you re-attempt up to three subjects with the better score counting. That gives you two genuine attempts — and makes timed practice between February and May worth far more than it used to be.

6 solved questions from this paper

Answer and worked explanation shown for each. The remaining 24 are timed and scored when you sign in free.

Q1Easy
The reaction 2Mg + O₂ → 2MgO is an example of a:
A.decomposition reaction
B.displacement reaction
C.combination reaction✓ Correct
D.double displacement reaction
Answer: C. combination reaction
Explanation: Two substances combine to form a single product, which is a combination reaction.
Q2Easy
The pH of a neutral solution at 25 °C is:
A.7✓ Correct
B.14
C.1
D.0
Answer: A. 7
Explanation: A neutral solution has equal H⁺ and OH⁻ concentrations, giving a pH of 7.
Q3Easy
Which gas is evolved when dilute hydrochloric acid reacts with zinc granules?
A.Carbon dioxide
B.Hydrogen✓ Correct
C.Oxygen
D.Chlorine
Answer: B. Hydrogen
Explanation: Zn + 2HCl → ZnCl₂ + H₂; hydrogen gas is released, which burns with a 'pop' sound.
Q4Medium
Which of the following is a decomposition reaction?
A.2H₂O → 2H₂ + O₂✓ Correct
B.Zn + CuSO₄ → ZnSO₄ + Cu
C.CaO + H₂O → Ca(OH)₂
D.NaOH + HCl → NaCl + H₂O
Answer: A. 2H₂O → 2H₂ + O₂
Explanation: A single compound (water) breaks down into simpler substances, which is decomposition.
Q5Medium
Assertion (A): Tooth decay begins when the pH of the mouth falls below 5.5. Reason (R): Bacteria in the mouth produce acids by the degradation of sugar and food particles. Choose the correct option.
A.Both A and R are true but R is not the correct explanation of A
B.Both A and R are true and R is the correct explanation of A✓ Correct
C.A is true but R is false
D.A is false but R is true
Answer: B. Both A and R are true and R is the correct explanation of A
Explanation: The acids produced by bacteria lower the mouth's pH below 5.5, which corrodes enamel — so R correctly explains A.
Q6Medium
Which of the following metals is generally found in the free (native) state in nature?
A.Iron
B.Sodium
C.Gold✓ Correct
D.Aluminium
Answer: C. Gold
Explanation: Gold is very unreactive (low in the reactivity series), so it occurs uncombined in nature.

Sit the full paper — free

All 30 questions on a 60-minute timer, scored automatically, with a worked solution for every one — including the 24 not shown above. Sign in with Google — no card needed.

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More Class 10 Science board papers

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Questions students ask about this paper

Is this an official CBSE sample paper?

No — and that is deliberate. This is an original paper written in the CBSE board pattern by our subject team, not a copy of CBSE's official Sample Question Paper. It means you get fresh questions you have not already seen on a dozen other sites, with instant scoring and worked solutions rather than a PDF.

How is this Class 10 Science paper marked?

+1 for a correct answer and 0 for a wrong one — no negative marking, exactly like the real board paper. So attempt every question — there is no penalty for a wrong answer on a board paper, and leaving a question blank can only cost you.

How long should this paper take?

60 minutes for 30 questions, roughly 120 seconds each. The timer runs whether or not you are watching it, which is the point: board marks are lost to pacing at least as often as to gaps in knowledge.

Do I need to pay to attempt it?

No. Sign in free with Google and the full paper opens with a live timer, automatic scoring and a worked solution for every question — including the ones not shown on this page.

Does the May 2027 improvement exam change how I should practise?

It raises the value of timed practice. Because the better of your two scores counts, a February attempt that goes badly is no longer final — but only if you know precisely which topics cost you the marks. A scored full-length paper tells you that; re-reading the chapter does not.

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