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

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 picks 30 objective questions from a pool of 31 questions covering the whole Class 10 Science syllabus. So when you take it again, you get a different paper, not the same questions.

The difficulty mix is 15 Easy · 16 Medium, balanced the way the board balances Section A. You get 60 minutes, about 120 seconds a question, which is the speed the real paper needs. 6 of the questions are solved in full below, each with the correct option and a worked explanation. Sign in free to attempt the other 24, timed and scored.

From 2026-27, CBSE Class 10 has two board exams a year. The first, around 15 February – 10 March 2027, is compulsory. An optional improvement exam in May 2027 lets you take up to three subjects again, and the better score counts. So you get two real attempts, and timed practice between February and May matters far more than it used to.

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

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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 on purpose. This is an original paper written by our subject team in the CBSE board pattern. It is not a copy of CBSE's official Sample Question Paper. So you get fresh questions you have not already seen on a dozen other sites, with instant scoring and worked solutions instead of 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. A board paper takes nothing away for a wrong answer, and leaving a question blank can only cost you.

How long should this paper take?

60 minutes for 30 questions, about 120 seconds each. The timer keeps running whether you watch it or not, and that is the point. Students lose board marks to poor timing at least as often as to gaps in what they know.

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 makes timed practice more useful. The better of your two scores counts, so a February attempt that goes badly is no longer final. But that only helps if you know exactly which topics cost you marks. A scored full-length paper tells you that. Re-reading the chapter does not.

All Class 10 subjects, chapters and mock tests →