CBSE Class 10 Science MCQ Practice 2025-26

60 interactive MCQs from the CBSE Sample Question Paper 2025-26 and the official Case Study Question Bank. Click any option for instant feedback, a full explanation, and score tracking.

60 Questions 29 Biology 28 Chemistry 3 Physics Source: CBSE Official

Attempted

Correct ✓

Wrong ✗

Score

00:00

Biology — Chapter 6 Life Processes

SQP Q1

Select the group in which all organisms have the same mode of nutrition.

✅ Explanation

All organisms in option C are parasites — they obtain nutrition from a living host. Cuscuta is a plant parasite; ticks, lice, leeches, and tapeworm are animal parasites. The other options mix autotrophs (Cactus, grass) and decomposers (yeast) with parasites.

SQP Q2

Which of the following indicates the products formed after breakdown of glucose in muscle cells when there is lack of oxygen?

✅ Explanation

In muscle cells, anaerobic respiration produces lactic acid + Energy (C₆H₁₂O₆ → 2C₃H₆O₃ + Energy). Ethanol + CO₂ is the pathway used by yeast, not muscle cells. CO₂ + Water + Energy is aerobic respiration.

Biology — Chapter 7 Control and Coordination

SQP Q3

Which of the following is a correct combination of function and part of the brain?

✅ Explanation

The medulla oblongata in the hindbrain controls involuntary actions like blood pressure, heartbeat, and breathing. Posture and balance are controlled by the cerebellum; hunger by the hypothalamus; and salivation by the medulla (not midbrain).

SQP Q4

The blood glucose level in a patient was very high. It may be due to inadequate secretion of:

✅ Explanation

Insulin is secreted by the β-cells (islets of Langerhans) of the pancreas. It lowers blood glucose by promoting its uptake by cells. Insufficient insulin leads to high blood glucose — the hallmark of diabetes mellitus. Note: insulin comes from the pancreas, NOT the pituitary gland.

Biology — Chapter 8 Heredity and Evolution

SQP Q5

In a cross between black-furred rabbit (B) and white-furred rabbit (b), all offspring were found to have black fur. What can be inferred about the genetic makeup of the parent rabbits?

✅ Explanation

If all offspring show black fur, one parent must be homozygous dominant (BB) and the other homozygous recessive (bb). All offspring are Bb — they express the dominant allele (black). In Bb×Bb, some white-furred offspring would appear. In Bb×bb, half would be white.

SQP Q8 (A&R)

Assertion (A): Tallness of a pea plant is controlled by an enzyme.
Reason (R): The gene for that enzyme makes proteins which help the plant to be tall.

✅ Explanation

Both statements are true. Genes produce specific enzymes/proteins — the gene for tallness produces an enzyme that synthesises plant growth hormones (gibberellins), causing the plant to grow tall. R correctly explains A, making it the correct explanation.

Biology — Chapter 15 Our Environment

SQP Q6

Which are the correct statements related to ozone?
(i) Ozone layer helps in increasing UV radiations reaching Earth.
(ii) Ozone is a deadly poison.
(iii) Ozone layer shields the Earth from UV radiations.
(iv) Ozone layer prevents UV rays which cause skin cancer.
(v) Ozone is formed with the help of chlorofluorocarbons.

✅ Explanation

Statements (ii), (iii), and (iv) are correct. Statement (i) is wrong — the ozone layer blocks UV radiation, not increases it. Statement (v) is wrong — CFCs actually destroy ozone (each CFC molecule can destroy thousands of ozone molecules).

SQP Q7

Which of the following human activities has resulted in an increase of non-biodegradable substances?

✅ Explanation

Plastic is a synthetic polymer that is non-biodegradable. Its widespread use as packaging material has massively increased non-biodegradable waste in the environment. Organic farming, tree plantation, and composting all involve biodegradable materials.

SQP Q9 (A&R)

Assertion (A): Vulture will always have the least amount of pesticides in a food chain.
Reason (R): Vulture occupies the last trophic level and it gets only 10% of energy of the previous trophic level.

✅ Explanation

The Assertion is FALSE — due to biological magnification, organisms at higher trophic levels accumulate more pesticides, not less. Vultures (at the top) would have the most concentrated pesticides. The Reason is TRUE — the 10% energy transfer law is correct. Hence D: A is false but R is true.

Biology — Question Bank Our Environment — Case Study: Food Chains & Energy Flow Answer any 4 in the CBSE exam; practise all 5 here.

📖 Case Study

Food Chains and Energy Flow
Food chains are very important for the survival of most species. When only one element is removed from the food chain it can result in extinction of a species in some cases. The foundation of the food chain consists of primary producers (autotrophs) that convert solar energy or chemical energy into complex organic compounds. All other organisms depend on this primary production.

Q10

Question Bank — Case 6

If 10,000 J of solar energy falls on green plants in a terrestrial ecosystem, what amount of solar energy will be converted into food energy?

✅ Explanation

Plants capture approximately 1% of the total solar energy falling on them and convert it into food (chemical) energy. 1% of 10,000 J = 100 J. This is a two-step inefficiency: plants absorb ~10% of light energy, and of that ~10% is stored as food energy, giving 10% × 10% = 1%.

Q11

Question Bank — Case 6

If Ravi is consuming curd/yogurt for lunch, which trophic level in a food chain should he be considered as occupying?

✅ Explanation

Curd is made from milk (from cows/buffaloes). The food chain is: Grass (1st) → Cow (2nd) → Ravi eating curd (3rd). So Ravi is at the third trophic level. If he ate the cow directly, he would be at the second level.

Q12

Question Bank — Case 6

Decomposers are not included in the food chain. The correct reason is because decomposers:

✅ Explanation

Decomposers (bacteria, fungi) break down dead organic matter at every trophic level simultaneously — they decompose dead producers, herbivores, and carnivores alike. This makes it impossible to assign them to a single trophic level in a linear food chain.

Q13

Question Bank — Case 6

Matter and energy are two fundamental inputs of an ecosystem. Which statement correctly describes their movement?

✅ Explanation

Energy flow is unidirectional: Sun → Producers → Consumers → Lost as heat. It cannot be recycled back. Matter (nutrients) cycles repeatedly through biotic and abiotic components via decomposition, nutrient cycling, water cycle, etc.

Q14

Question Bank — Case 6

Which of the following limits the number of trophic levels in a food chain?

✅ Explanation

At each trophic level, only 10% of energy is transferred to the next level (90% is lost as heat). By the 4th or 5th trophic level, the available energy is so little (0.1% of original) that sustaining another consumer level becomes thermodynamically impossible.

Biology — Question Bank Our Environment — Case Study: Aquatic Ecosystem Answer any 4 in the CBSE exam; practise all 5 here.

📖 Case Study

Seashore Aquatic Food Web
Observe the following seashore food web:
Microscopic animals → Mussel → Crab → Dogfish
Microscopic animals → Barnacle → Dogwhelk → Dogfish
Microscopic animals → Peri → Dogwhelk
In this web, microscopic animals are the primary producers/prey, and the arrows indicate energy flow.

Q15

Question Bank — Case 7

In the seashore food web, the mussel can be described as a:

✅ Explanation

In the food web, mussels feed on microscopic animals (which are primary consumers of microscopic algae/plants). So mussels are secondary consumers (3rd trophic level). Producers → Microscopic animals (1°) → Mussel (2°) → Crab (3°) → Dogfish (4°).

Q16

Question Bank — Case 7

Which trophic level is incorrectly defined?

✅ Explanation

Molds, yeast, and mushrooms are decomposers (saprophytes), not omnivores. Omnivores are organisms that eat both plants and animals (e.g., humans, bears, pigs). The other definitions are correct.

Q17

Question Bank — Case 7

The figure shows: Sun ☀ → Grass → Grasshopper → Frog → Snake. This food chain best represents:

✅ Explanation

A food chain starting with grass → grasshopper → frog → snake is the classic example of a grassland food chain. It begins with a terrestrial grass producer and involves terrestrial consumers typical of grassland/meadow ecosystems.

Q18

Question Bank — Case 7

Why do all food chains start with plants?

✅ Explanation

Plants are autotrophs/producers — they capture solar energy through photosynthesis and convert it into chemical energy (food). All other organisms are heterotrophs that depend on this primary production. Plants are the entry point of solar energy into the ecosystem.

Q19

Question Bank — Case 7

In a food web with organisms A, B, C, D, E, F, G where: A is the base, B and D both feed on A's products, C feeds on B, F feeds on B and D, G is at the top fed by C, D, E, and F — which two organisms are competing for food?

✅ Explanation

B and D both feed from the same food source (A's products) at the same trophic level, making them competitors. Competition occurs between organisms at the same trophic level that consume the same prey species.

Biology — Question Bank Our Environment — Case Study: Waste Management Answer any 4 in the CBSE exam; practise all 5 here.

📖 Case Study

Waste Management — The 5 R's
You must have come across the 5 R's to save the environment: Refuse, Reduce, Reuse, Repurpose and Recycle. This hierarchy guides how we should handle waste, from best (refusing unnecessary items) to least preferred (recycling). Effective waste management is critical as global waste generation is doubling due to population growth.

Q20

Question Bank — Case 8

Choose the waste management strategy that is matched with its correct example.

✅ Explanation

Repurposing = using a waste item for a new, different purpose (plastic bottle → flower pot). Refuse = refusing single-use plastics; Reduce = choosing less packaged products; Reuse = giving unwanted items to others for the same purpose.

Q21

Question Bank — Case 8

Recycling of paper is a good practice, but recycled paper should not be used as food packaging because:

✅ Explanation

Recycled paper may contain traces of inks, dyes, and other contaminants from its previous use. These can migrate into food and cause infections or health hazards. Food packaging requires virgin (unrecycled) food-grade paper to ensure safety.

Q22

Question Bank — Case 8

According to the Solid Waste Management Rule 2016, which row correctly categorises wet waste, dry waste, and hazardous waste?

✅ Explanation

Option B is correct: Wet waste = biodegradable organic matter (coffee, tea, garden waste). Dry waste = recyclables (plastic, paper, cardboard). Hazardous waste = items requiring special disposal (expired medicines, razors, paint cans). Option C incorrectly places coffee/tea grounds as dry waste.

Q23

Question Bank — Case 8

Select the appropriate statements giving the importance of waste segregation:
(i) Less waste goes to the landfills (ii) Better for public health and the environment (iii) Helps in reducing the waste (iv) Results in deterioration of a waste picker's health

✅ Explanation

Statements (i) and (ii) are the correct reasons: proper segregation ensures recyclables are recycled (reducing landfill burden) and hazardous waste is safely handled (protecting public health and the environment). Statement (iv) is a negative consequence of poor segregation, not an importance of doing it right.

Q24

Question Bank — Case 8

When recycling a plastic water bottle, what should you do with the plastic cap?

✅ Explanation

Bottle caps are typically made of a different type of plastic (PP/HDPE) than the bottle (PET) and can jam recycling machinery or contaminate the recycling stream. The standard guidance is: cap in garbage, bottle in recycling.

Biology — Question Bank Sources of Energy — Biogas Plant Answer any 4 in the CBSE exam; practise all 5 here.

📖 Case Study

Biogas Plant
A biogas plant produces gas by fermenting biomass. The plant has four main parts: A = Inlet (slurry inlet), B = Digester (underground tank where anaerobic fermentation occurs), C = Outlet (overflow tank for spent slurry/manure), and D = Gas holder/dome (collects the produced gas). Bacteria break down organic waste in the digester, producing biogas (mainly methane) and nutrient-rich slurry.

Q25

Question Bank — Case 5

In which part of the biogas plant would you find anaerobic bacteria?

✅ Explanation

Anaerobic bacteria reside in the digester (B), where organic waste (dung + water slurry) is broken down in the absence of oxygen. The digester is sealed to maintain anaerobic conditions essential for methane-producing bacteria (methanogens).

Q26

Question Bank — Case 5

Which one of the following is NOT correct for biogas?

✅ Explanation

Biogas IS a renewable energy source because it is produced from organic waste (animal dung, agricultural residue) which is continuously available. The other statements are correct: biogas is carbon neutral (CO₂ released = CO₂ absorbed by the biomass), depends on anaerobic bacteria, and the leftover slurry is nutrient-rich manure.

Q27

Question Bank — Case 5

Which sequence correctly indicates the steps of anaerobic digestion in a biogas plant?

✅ Explanation

The correct sequence is: Organic waste (feed) → Digester (anaerobic bacteria break it down) → Biogas produced → Stored in gas holder → Used in generator/stove. Option D incorrectly suggests biogas is produced before the digestion step.

Q28

Question Bank — Case 5

Biogas is a better fuel than animal dung cake because:
(i) Biogas has lower calorific value. (ii) Animal dung cake has higher calorific value. (iii) Biogas has high heating capacity. (iv) Biogas burns without smoke.

✅ Explanation

Statements (iii) and (iv) are correct: biogas has a high calorific value (mainly CH₄) and burns cleanly without smoke, unlike dung cakes which produce smoke and particulate matter. Statements (i) and (ii) are false — biogas has higher, not lower, calorific value than dung cake.

Q29

Question Bank — Case 5

Biogas is formed in the:

✅ Explanation

Biogas production is an anaerobic process — it requires the absence of air (oxygen). Water is needed as a medium for the slurry and for the metabolic activities of anaerobic bacteria. Hence: presence of water + absence of air.

Chemistry — Chapter 1 Chemical Reactions and Equations

Q30

SQP Q17

Which of the following equations represent redox reactions and what are the values for p and q?
Equation 1: Fe₂O₃(s) + 2Al(s) → Al₂O₃(s) + p Fe(l) + heat
Equation 2: 2C₄H₁₀(g) + 13O₂(g) → 8CO₂(g) + q H₂O(g)

✅ Explanation

Both are redox reactions. Eq 1: Fe₂O₃ + 2Al → Al₂O₃ + 2Fe. Fe is reduced (+3→0), Al is oxidised (0→+3). p = 2. Eq 2: Combustion of butane. Balance: 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O. C is oxidised, O₂ is reduced. q = 10.

Q31

SQP Q23

In the reaction of aqueous barium chloride with aqueous sodium sulphate, the aqueous solution formed will be:

✅ Explanation

BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄↓ + 2NaCl(aq). BaSO₄ is insoluble and precipitates out. The remaining aqueous solution contains NaCl. This is a double displacement (precipitation) reaction.

Chemistry — Question Bank Chemical Reactions — Case Study: Marble & CaCO₃ Answer any 4 in the CBSE exam; practise all 5 here.

📖 Case Study

Marble, CaCO₃, and Chemical Reactions
Marble's popularity began in ancient Rome and Greece, where it was used to construct massive pillars and sculptures. Marble is primarily composed of calcium carbonate (CaCO₃). When heated, CaCO₃ undergoes thermal decomposition: CaCO₃(s) → CaO(s) + CO₂(g). A student heated 10 g of CaCO₃ in a sealed container and noted pressure readings every 5 minutes, observing the steepest pressure increase in the 0–5 minute interval.

Q32

Question Bank — Case 1

The substance not likely to contain CaCO₃ is:

✅ Explanation

Calcined gypsum (plaster of Paris) is CaSO₄·½H₂O — it contains calcium sulphate, not calcium carbonate. Dolomite is CaMg(CO₃)₂, marble is CaCO₃, and sea shells are primarily CaCO₃.

Q33

Question Bank — Case 1

A student plotted pressure vs time while heating CaCO₃ in a sealed container. Based on a graph showing the steepest pressure increase in the first interval, during which time interval did maximum decomposition take place?

✅ Explanation

The steepest rise in pressure in the graph occurs in the 0–5 minute interval. Since the pressure increase results from CO₂ gas produced by the thermal decomposition of CaCO₃, the maximum rate of decomposition occurs in the first 5 minutes when the reaction is fastest.

Q34

Question Bank — Case 1

Gas A (CO₂) obtained from decomposition of CaCO₃ is a reactant for an important biochemical process that occurs in the presence of sunlight. This process is:

✅ Explanation

CO₂ is the key reactant in photosynthesis: 6CO₂ + 6H₂O sunlight→ C₆H₁₂O₆ + 6O₂. This process occurs in green plants in the presence of sunlight. Respiration uses O₂ and produces CO₂ (reverse direction).

Q35

Question Bank — Case 1

Marble statues are corroded when they repeatedly come into contact with polluted rain water. Identify the main reason.

✅ Explanation

Polluted rainwater (acid rain) contains dissolved acidic gases like SO₂ and NO₂, making it acidic. This reacts with CaCO₃: CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. The marble dissolves and corrodes over time.

Q36

Question Bank — Case 1

Calcium oxide can be reduced to calcium by heating with sodium metal. Which compound acts as the oxidising agent in this process?

✅ Explanation

In this reaction: CaO + 2Na → Ca + Na₂O.
CaO is reduced (Ca²⁺ → Ca⁰, gains electrons) → CaO is the oxidising agent.
Sodium is oxidised (Na⁰ → Na⁺, loses electrons) → Na is the reducing agent.

Chemistry — Question Bank Chemical Reactions — Case Study: MnO₂ & HCl (Redox) Answer any 4 in the CBSE exam; practise all 5 here.

📖 Case Study

Reaction of MnO₂ with HCl — Bleaching Powder
The reaction between MnO₂ and HCl is: MnO₂ + 4HCl → MnCl₂ + Cl₂↑ + 2H₂O. A gas with bleaching abilities (Cl₂) is released. This reaction is used in understanding redox chemistry and the industrial production of chlorine and bleaching powder.

Q37

Question Bank — Case 2

The chemical reaction between MnO₂ and HCl is an example of:

✅ Explanation

MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O.
Mn is reduced: +4 → +2 (in MnCl₂).
Cl is oxidised: −1 → 0 (in Cl₂).
Since both oxidation and reduction occur, this is a redox (oxidation-reduction) reaction.

Q38

Question Bank — Case 2

Chlorine gas reacts with __________ to form bleaching powder.

✅ Explanation

Bleaching powder is made by passing Cl₂ gas over dry slaked lime Ca(OH)₂:
2Ca(OH)₂ + 2Cl₂ → Ca(OCl)₂ + CaCl₂ + 2H₂O.
Dry Ca(OH)₂ is used (not solution) as the product is a dry powder. CaO (quicklime) is different from Ca(OH)₂ (slaked lime).

Q39

Question Bank — Case 2

Identify the correct statement about the reaction of MnO₂ with HCl:

✅ Explanation

In MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O:
• Mn: +4 → +2 (gains electrons = reduced) → MnO₂ is the oxidising agent.
• Cl: −1 → 0 (in Cl₂, loses electrons = oxidised) → HCl is the reducing agent.

Q40

Question Bank — Case 2

In the above reaction (MnO₂ + HCl), the nature of MnO₂ is:

✅ Explanation

MnO₂ (manganese dioxide) is a basic oxide — it is a metal oxide. Metal oxides are generally basic in nature. In this reaction, it acts as an oxidising agent and is reduced to MnCl₂.

Q41

Question Bank — Case 2

What will happen if we take dry HCl gas instead of aqueous solution of HCl in the reaction with MnO₂?

✅ Explanation

The reaction between MnO₂ and HCl requires free H⁺ and Cl⁻ ions, which are present only in aqueous HCl. Dry HCl gas does not ionise and lacks these free ions. Without ions, the redox reaction cannot proceed.

Chemistry — Chapter 2 Acids, Bases and Salts

Q42

SQP Q20

Methyl orange is added to dilute hydrochloric acid and to aqueous sodium hydroxide. What is the colour of methyl orange in each solution?

✅ Explanation

Methyl orange is a pH indicator: Red in acidic solutions (pH < ~3.1) and Yellow in neutral/alkaline solutions (pH > ~4.4). Dilute HCl is acidic → red; NaOH is alkaline → yellow.

Q43

SQP Q21

Which of the following substances, when dissolved in equal volumes of water, will have the highest pH?

✅ Explanation

Sodium hydroxide (NaOH) is a strong alkali that fully dissociates in water, producing maximum OH⁻ ions and a pH close to 14. Mg(OH)₂ is a weak/sparingly soluble base with lower pH. Sulphuric and acetic acids are acidic (pH < 7).

Q44

SQP Q22

When excess carbon dioxide is passed through lime water, the milkiness disappears because:

✅ Explanation

Step 1: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O (milky — CaCO₃ is insoluble).
Step 2 (excess CO₂): CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂ (soluble — milkiness disappears). Ca(HCO₃)₂ dissolves and the solution becomes clear.

Chemistry — Question Bank Acids, Bases and Salts — Case Study: Frothing in Yamuna Answer any 4 in the CBSE exam; practise all 5 here.

📖 Case Study

Frothing in Yamuna River
The Yamuna river frequently develops toxic white foam/froth due to high phosphate content from detergents used in dyeing industries, dhobi ghats, and households. Detergents are sodium salts of organic sulphonic acids and are basic (alkaline) in nature. Yamuna's pollution level is so severe that parts are labelled 'dead zones' with no dissolved oxygen for aquatic life.

Q45

Question Bank — Case 4

Predict the pH value of Yamuna river water if the cause of froth is high concentration of dissolved detergents.

✅ Explanation

Detergents are basic (alkaline) in nature. High concentrations of detergents would make the river water strongly alkaline with pH 10–11. A neutral solution has pH 7, acidic is below 7, and alkaline is above 7.

Q46

Question Bank — Case 4

Which statement is correct for water with detergents dissolved in it?

✅ Explanation

Detergent solution is basic/alkaline. In any basic solution: [OH⁻] is high (alkalis dissociate to give OH⁻ ions) and [H₃O⁺] is low (since pH is high). At 25°C, [H₃O⁺][OH⁻] = 10⁻¹⁴, so they are inversely related.

Q47

Question Bank — Case 4

The pH values of four solutions are: P = 2, Q = 9, R = 5, S = 11. Which correctly represents these solutions in increasing order of hydronium ion (H₃O⁺) concentration?

✅ Explanation

Lower pH = higher [H₃O⁺]. So: pH 11 (S) has least H₃O⁺ → pH 9 (Q) → pH 5 (R) → pH 2 (P) has most H₃O⁺.
Increasing order: S < Q < R < P. ✓

Q48

Question Bank — Case 4

High content of phosphate ions in river Yamuna may lead to:

✅ Explanation

High phosphate causes eutrophication: excessive algae blooms grow rapidly (⬆ algae). When algae die and decompose, bacteria consume large amounts of dissolved oxygen (⬇ DO), creating "dead zones" where aquatic life cannot survive.

Q49

Question Bank — Case 4

If a sample of water containing detergents (basic/alkaline) is provided to you, which method will you adopt to neutralise it?

✅ Explanation

Detergent water is basic. To neutralise a base, we need an acid. Vinegar is a dilute solution of acetic acid (CH₃COOH) and will neutralise the base. Baking soda (NaHCO₃), caustic soda (NaOH), and washing soda (Na₂CO₃) are all basic — they would not neutralise a basic solution.

Chemistry — Chapter 3 Metals and Non-metals

Q50

SQP Q18

Which two of the following statements about reactions of oxides with dilute HCl and aqueous NaOH are correct?
I. Aluminium oxide reacts with both dilute HCl and NaOH.
II. Calcium oxide reacts with both dilute HCl and NaOH.
III. Zinc oxide reacts with both dilute HCl and NaOH.
IV. Sulphur dioxide does not react with either HCl or NaOH.

✅ Explanation

Al₂O₃ and ZnO are amphoteric oxides — they react with both acids AND bases (I ✓ and III ✓).
CaO is a basic oxide — reacts with acids only, NOT bases (II ✗).
SO₂ is an acidic oxide — reacts with bases (NaOH), NOT acids (IV ✗).

Q51

SQP Q19

An iron nail is added to aqueous copper (II) sulphate (P) and aqueous silver nitrate (Q). Which observation is correct?

✅ Explanation

Iron is more reactive than both Cu and Ag (reactivity: Fe > Cu > Ag).
In P: Fe + CuSO₄ → FeSO₄ + Cu↓ → brown copper coating on iron nail.
In Q: Fe + 2AgNO₃ → Fe(NO₃)₂ + 2Ag↓ → silver coating on iron nail.

Chemistry — Chapter 4 Carbon and its Compounds

Q52

SQP Q24 (A&R)

Assertion (A): C₄H₈, C₄H₆ and C₄H₁₀ are members of the same homologous series.
Reason (R): C₄H₈, C₄H₆, C₃H₄, C₃H₆, C₂H₄, C₂H₂ are unsaturated hydrocarbons.

✅ Explanation

Assertion is FALSE: C₄H₁₀ (CₙH₂ₙ₊₂) is an alkane; C₄H₈ (CₙH₂ₙ) is an alkene; C₄H₆ (CₙH₂ₙ₋₂) is an alkyne/diene. They belong to different homologous series.
Reason is TRUE: All the listed compounds (CₙH₂ₙ and CₙH₂ₙ₋₂ series) are indeed unsaturated hydrocarbons with at least one double or triple bond.

Chemistry — Question Bank Carbon and its Compounds — Case Study: Fuel Combustion Answer any 4 in the CBSE exam; practise all 5 here.

📖 Case Study

Chemistry in Automobiles — Combustion of Fuel
Internal combustion engines convert the chemical energy stored in hydrocarbon fuels into mechanical energy. An electrical spark ignites the fuel-air mixture. Complete combustion of gasoline (C₈H₁₈) in full supply of air: 2C₈H₁₈(l) + 25O₂(g) → 16CO₂(g) + 18H₂O(g). Incomplete combustion (limited air) produces CO (carbon monoxide) and soot (carbon particles) — the cause of black exhaust smoke.

Q53

Question Bank — Case 3

Which are the products obtained from the complete combustion of gasoline (2C₈H₁₈ + 25O₂ →)?
Product X and Product Y are:

✅ Explanation

Complete combustion of any hydrocarbon in excess oxygen always produces CO₂ and H₂O. 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O. CO (option B) is a product of incomplete combustion only.

Q54

Question Bank — Case 3

Identify the types of chemical reaction occurring during the combustion of fuel:

✅ Explanation

Combustion is:
• Oxidation: fuel (carbon compound) reacts with O₂ (oxygen is gained).
• Exothermic: heat and light energy are released (ΔH is negative).
It is NOT endothermic (which absorbs heat) nor decomposition (which breaks one compound).

Q55

Question Bank — Case 3

On the basis of energy evolution/absorption, which of the following processes are similar to combustion of fuel?
(i) Photosynthesis in plants (ii) Respiration in the human body (iii) Decomposition of vegetable matter (iv) Decomposition of ferrous sulphate

✅ Explanation

Combustion is exothermic. Processes that are also exothermic (release energy):
• (ii) Respiration: C₆H₁₂O₆ + O₂ → CO₂ + H₂O + Energy ✓
• (iii) Decomposition of vegetable matter: releases heat ✓
(i) Photosynthesis is endothermic; (iv) Decomposition of FeSO₄ is endothermic.

Q56

Question Bank — Case 3

A student observed a cloud of black smoke from the exhaust of moving trucks. Choose the correct reason for black smoke production:

✅ Explanation

Black smoke = soot (unburnt carbon particles). It forms during incomplete combustion when the supply of air (oxygen) is limited. In a diesel engine under heavy load, the fuel-to-air ratio is high, causing incomplete combustion: fuel → CO + C (soot) + H₂O.

Q57

Question Bank — Case 3

Although nitrogen is the most abundant gas in the atmosphere, it does not take part in combustion. Identify the correct reason:

✅ Explanation

Nitrogen (N₂) has an extremely strong triple bond (N≡N), making it very stable and chemically inert under normal combustion conditions. The bond dissociation energy is ~941 kJ/mol — too high to break during typical combustion temperatures.

Physics — Chapter 10 Light — Reflection and Refraction

Q58

SQP Q30

Arnav wrote these statements about reflection from curved mirrors. Choose the option listing the correct statements:
I. Concave mirrors can produce both real and virtual images depending on object position.
II. Convex mirrors always produce real, inverted images regardless of object position.
III. In both concave and convex mirrors, 1/f = 1/v + 1/u applies.

✅ Explanation

I ✓: Concave mirrors form real/inverted images when object is beyond F, and virtual/erect when object is between F and mirror.
II ✗: Convex mirrors always form virtual, erect, diminished images — never real or inverted.
III ✓: The mirror formula 1/f = 1/v + 1/u applies to both types of spherical mirrors.

Q59

SQP Q32 (A&R)

Assertion (A): A point object is placed at a distance of 26 cm from a convex mirror of focal length 26 cm. The image will not form at infinity.
Reason (R): For the above system, the equation 1/f = 1/v + 1/u gives v = ∞.

✅ Explanation

A is TRUE: For a convex mirror, f = +26 cm, u = −26 cm. Using 1/f = 1/v + 1/u: 1/26 = 1/v − 1/26 → 1/v = 2/26 → v = +13 cm. Image forms at 13 cm (NOT at infinity).
R is FALSE: The equation gives v = 13 cm, not infinity.
Hence: C — A is true but R is false.

Physics — Chapter 11 The Human Eye and the Colourful World

Q60

SQP Q31

Choose the correct option that explains why we perceive the daytime sky as blue.

✅ Explanation

Rayleigh scattering: the intensity of scattered light is inversely proportional to λ⁴ (scattering ∝ 1/λ⁴). Blue light (λ ≈ 450 nm) scatters far more than red light (λ ≈ 700 nm). Our eyes are more sensitive to blue than violet (which also scatters a lot), making the sky appear blue.