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Haryana BSEH Secondary Science study materials
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Haryana BSEH Secondary Science practice questions

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Question 1Chemical Substances and Processes

Which gas is released when dilute hydrochloric acid reacts with zinc granules?

  1. Oxygen
  2. Carbon dioxide
  3. Hydrogen Correct answer.
  4. Chlorine

Explanation

Zinc is more reactive than hydrogen, so it displaces hydrogen from the acid, forming zinc chloride and hydrogen gas. The gas burns with a pop sound, which is the standard test for hydrogen. Carbon dioxide is released only when a carbonate reacts with acid.

Question 2Chemical Substances and Processes

A blue litmus paper is dipped into a solution and turns red. What does this observation show about the solution?

  1. It is neutral.
  2. It is basic.
  3. It is acidic. Correct answer.
  4. It contains only water.

Explanation

Litmus is red in acidic solutions and blue in basic solutions. Since blue litmus turns red, the solution must be acidic, meaning its hydrogen ion concentration exceeds that of a neutral solution. Basic solutions turn red litmus blue instead.

Question 3Chemical Substances and Processes

Which of the following is the correct chemical formula of washing soda?

  1. Na2CO3·10H2O Correct answer.
  2. NaOH
  3. NaHCO3
  4. NaCl

Explanation

Washing soda is hydrated sodium carbonate, written as Na2CO3·10H2O, and it is used to soften hard water. Baking soda is NaHCO3, caustic soda is NaOH, and common salt is NaCl, so these are different substances.

Question 4Chemical Substances and Processes

In the reaction CuO + H2 → Cu + H2O, which substance is oxidised?

  1. CuO
  2. H2 Correct answer.
  3. H2O
  4. Cu

Explanation

Oxidation is loss of hydrogen or gain of oxygen. Hydrogen in H2 loses its place to oxygen and becomes water, so hydrogen is oxidised while copper(II) oxide is reduced to copper.

Question 5Chemical Substances and Processes

Which property of metals allows them to be beaten into thin sheets?

  1. Ductility
  2. Conductivity
  3. Malleability Correct answer.
  4. Sonority

Explanation

Malleability is the ability of a metal to be hammered or rolled into thin sheets without breaking. Ductility refers to drawing into wires, conductivity to heat and electricity, and sonority to ringing when struck.

Question 6Chemical Substances and Processes

Which of the following is a natural source of the acid commonly called vinegar?

  1. Sting of an ant
  2. Lemon juice
  3. Vinegar from fermentation of sugar solution Correct answer.
  4. Curd

Explanation

Vinegar is a dilute solution of ethanoic acid obtained by fermenting sugar solutions or fruit juices. Lemon contains citric acid, curd contains lactic acid, and ant stings contain methanoic acid.

Question 7Chemical Substances and Processes

Which of the following reactions is a displacement reaction?

  1. AgNO3 + NaCl → AgCl + NaNO3
  2. NaOH + HCl → NaCl + H2O
  3. Fe + CuSO4 → FeSO4 + Cu Correct answer.
  4. CaCO3 → CaO + CO2

Explanation

In a displacement reaction a more reactive element pushes a less reactive one out of its compound. Iron is more reactive than copper, so it displaces copper from copper sulphate solution. The other options are precipitation, decomposition and neutralisation respectively.

Question 8Chemical Substances and Processes

What is the pH range of a strong acid on the pH scale?

  1. 5 to 6
  2. 0 to 3 Correct answer.
  3. 8 to 14
  4. 7 only

Explanation

The pH scale runs from 0 to 14, with values below 7 acidic and above 7 basic. Strong acids such as hydrochloric acid give pH values close to 0 to 3, while pH 7 is neutral.

Question 9Chemical Substances and Processes

Which of the following is the correct balanced equation for the reaction of sodium with water?

  1. Na + H2O → NaOH + H2
  2. 2Na + H2O → 2NaOH + H2
  3. Na + 2H2O → NaOH + 2H2
  4. 2Na + 2H2O → 2NaOH + H2 Correct answer.

Explanation

Balancing requires equal numbers of each atom on both sides. Two sodium atoms and two water molecules give two NaOH units and one hydrogen molecule, so 2Na + 2H2O → 2NaOH + H2 is correct. The other options leave atoms unbalanced.

Question 10Chemical Substances and Processes

A student adds dilute sulphuric acid to sodium hydroxide solution until the mixture is neutral. Which salt is formed in this reaction?

  1. Sodium sulphide
  2. Sodium hydrogencarbonate
  3. Sodium sulphite
  4. Sodium sulphate Correct answer.

Explanation

An acid reacting with a base gives a salt and water. Sulphuric acid with sodium hydroxide forms sodium sulphate and water, following the pattern metal hydroxide + acid → salt + water.

Question 11Chemical Substances and Processes

Which of the following statements correctly describes the corrosion of iron?

  1. It requires only oxygen and occurs faster in dry air.
  2. It requires both oxygen and moisture and is called rusting. Correct answer.
  3. It is prevented by coating the iron with a layer of common salt.
  4. It produces a black coating of iron oxide that protects the metal.

Explanation

Rusting is the corrosion of iron in the presence of both oxygen and water, forming hydrated iron(III) oxide. Dry air or pure oxygen alone slows or prevents it, and salt actually accelerates rusting rather than preventing it.

Question 12Chemical Substances and Processes

When a small piece of calcium is added to cold water, which observation is expected?

  1. It dissolves without any gas or heat change.
  2. It sinks and no gas is produced.
  3. It reacts only on heating to give carbon dioxide.
  4. It floats and reacts vigorously with a hissing sound, giving hydrogen. Correct answer.

Explanation

Calcium is reactive enough to displace hydrogen from cold water, but the reaction is less violent than with sodium. The metal floats because hydrogen bubbles stick to it, and the reaction releases hydrogen gas and heat.

Question 13Chemical Substances and Processes

Baking powder is used instead of baking soda in some recipes. What is the main advantage of baking powder?

  1. It contains both a carbonate and an acid, so it releases carbon dioxide without needing an added acid. Correct answer.
  2. It contains no base and therefore cannot react.
  3. It produces oxygen gas that makes the dough rise.
  4. It is a single compound that reacts only when heated to 200 °C.

Explanation

Baking powder is a mixture of sodium hydrogencarbonate and a solid edible acid such as tartaric acid. When moistened, the acid and carbonate react to release carbon dioxide, so the dough rises without adding an external acid.

Question 14Chemical Substances and Processes

Which of the following pairs of metals is arranged in order of decreasing reactivity?

  1. Magnesium, zinc, copper Correct answer.
  2. Copper, magnesium, zinc
  3. Copper, zinc, magnesium
  4. Zinc, magnesium, copper

Explanation

The reactivity series places magnesium above zinc and zinc above copper. Therefore the order of decreasing reactivity is magnesium, then zinc, then copper.

Question 15Chemical Substances and Processes

Which of the following is a decomposition reaction?

  1. AgNO3 + NaCl → AgCl + NaNO3
  2. Zn + 2HCl → ZnCl2 + H2
  3. 2H2 + O2 → 2H2O
  4. CaCO3 → CaO + CO2 Correct answer.

Explanation

A decomposition reaction is one in which a single compound breaks down into two or more simpler substances. Heating calcium carbonate gives calcium oxide and carbon dioxide, so this is decomposition.

Question 16Chemical Substances and Processes

Which of the following salts is acidic in nature when dissolved in water?

  1. Ammonium chloride Correct answer.
  2. Sodium carbonate
  3. Potassium nitrate
  4. Sodium chloride

Explanation

Salts of a strong acid with a weak base hydrolyse to give an acidic solution. Ammonium chloride comes from hydrochloric acid and ammonia, so its solution is acidic. Sodium salts of strong acids are neutral, and sodium carbonate is basic.

Question 17Chemical Substances and Processes

Which of the following substances is used in the laboratory to test for carbon dioxide gas?

  1. Sodium chloride solution
  2. Dilute hydrochloric acid
  3. Lime water Correct answer.
  4. Distilled water

Explanation

Carbon dioxide turns lime water milky because it forms insoluble calcium carbonate. Excess carbon dioxide can later dissolve the precipitate, but the milky appearance is the standard test.

Question 18Chemical Substances and Processes

A shiny iron nail is kept in copper sulphate solution for some time. Which observation is correct?

  1. A red-brown coating of copper appears on the nail and the blue colour fades. Correct answer.
  2. A white precipitate forms and the solution remains blue.
  3. The nail becomes silvery and the solution turns green.
  4. No change occurs because iron is less reactive than copper.

Explanation

Iron is more reactive than copper, so it displaces copper from copper sulphate. Copper deposits as a red-brown coating on the nail while iron(II) sulphate forms, and the blue colour of the solution fades.

Question 19Chemical Substances and Processes

What is the oxidation state of nitrogen in nitric acid, HNO3?

  1. -3
  2. +5 Correct answer.
  3. +1
  4. +3

Explanation

In HNO3, hydrogen is +1 and each oxygen is -2, giving a total of -6 from three oxygens. For the molecule to be neutral, nitrogen must be +5, since +1 + 5 - 6 = 0.

Question 20Chemical Substances and Processes

Which of the following statements about a salt formed from a weak acid and a strong base is correct?

  1. Its aqueous solution is basic and turns red litmus blue. Correct answer.
  2. Its aqueous solution is acidic and turns blue litmus red.
  3. It does not dissolve in water at all.
  4. Its aqueous solution is always neutral.

Explanation

The anion of a weak acid hydrolyses in water and produces hydroxide ions, making the solution basic. Sodium carbonate and sodium acetate are examples, and basic solutions turn red litmus blue.

Question 21Chemical Substances and Processes

In the reaction MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O, what is the role of manganese dioxide?

  1. It acts as a base and neutralises the acid.
  2. It acts as a catalyst and remains unchanged.
  3. It acts as a reducing agent and is oxidised.
  4. It acts as an oxidising agent and is reduced. Correct answer.

Explanation

Manganese in MnO2 has oxidation state +4 and becomes +2 in MnCl2, so it gains electrons and is reduced. The substance that is reduced oxidises the hydrochloric acid, so MnO2 is the oxidising agent.

Question 22Chemical Substances and Processes

Why does the reactivity of metals with dilute acids generally decrease across the reactivity series from magnesium to copper?

  1. Because the atomic masses of the metals increase steadily.
  2. Because the ionisation tendency of the metal atoms decreases, so they lose electrons less readily. Correct answer.
  3. Because the acids become less concentrated during the reaction.
  4. Because the metals become more dense and therefore sink in the acid.

Explanation

A metal reacts with an acid by losing electrons to hydrogen ions and forming positive ions. Metals high in the series lose electrons more readily, so the reaction is faster, while copper has little tendency to lose electrons and does not react with dilute acids.

Question 23Chemical Substances and Processes

What mass of sodium hydroxide is needed to neutralise exactly 0.1 mol of sulphuric acid according to 2NaOH + H2SO4 → Na2SO4 + 2H2O?

  1. 4.0 g
  2. 16.0 g
  3. 2.0 g
  4. 8.0 g Correct answer.

Explanation

The equation shows that two moles of NaOH are required per mole of sulphuric acid. For 0.1 mol of acid, 0.2 mol of NaOH is needed, and with a molar mass of 40 g/mol this is 0.2 × 40 = 8.0 g.

Question 24Chemical Substances and Processes

Which of the following statements about the reaction of a metal carbonate with a dilute acid is correct?

  1. It produces only water and no gas.
  2. It produces a salt, water and carbon dioxide, and the gas extinguishes a burning splint. Correct answer.
  3. It produces a salt and hydrogen, and the gas burns with a pop.
  4. It produces chlorine gas, which bleaches litmus.

Explanation

Metal carbonates react with dilute acids to give a salt, water and carbon dioxide, for example CaCO3 + 2HCl → CaCl2 + H2O + CO2. Carbon dioxide does not support combustion and therefore extinguishes a burning splint.

Question 25Chemical Substances and Processes

Which of the following is the correct order of pH for solutions of equal concentration of hydrochloric acid, acetic acid and sodium hydroxide?

  1. Hydrochloric acid < sodium hydroxide < acetic acid
  2. Hydrochloric acid < acetic acid < sodium hydroxide Correct answer.
  3. Sodium hydroxide < acetic acid < hydrochloric acid
  4. Acetic acid < hydrochloric acid < sodium hydroxide

Explanation

Hydrochloric acid is a strong acid and gives the lowest pH at equal concentration, while acetic acid is weak and gives a higher pH. Sodium hydroxide is a strong base, so its pH is highest, above 7.

Question 26Chemical Substances and Processes

Which gas is produced when dilute hydrochloric acid reacts with zinc granules?

  1. Oxygen
  2. Chlorine
  3. Hydrogen Correct answer.
  4. Carbon dioxide

Explanation

Zinc lies above hydrogen in the reactivity series, so it displaces hydrogen from the dilute acid: Zn + 2HCl → ZnCl2 + H2. The gas evolved burns with a pop sound, which is the standard laboratory test for hydrogen. Oxygen, chlorine and carbon dioxide are not formed in this metal-acid reaction.

Question 27Chemical Substances and Processes

Blue copper sulphate crystals turn white on gentle heating. Which type of salt is copper sulphate pentahydrate?

  1. Anhydrous salt
  2. Basic salt
  3. Double salt
  4. Hydrated salt Correct answer.

Explanation

A hydrated salt contains a fixed number of water molecules as water of crystallisation within its crystal lattice; CuSO4·5H2O is the standard example. Heating drives off this water and leaves the white anhydrous salt, and adding water restores the blue colour. This reversible colour change is used as a test for water.

Question 28Chemical Substances and Processes

Which of the following is the common name of the compound with formula NaHCO3?

  1. Bleaching powder
  2. Washing soda
  3. Baking soda Correct answer.
  4. Caustic soda

Explanation

NaHCO3 is sodium hydrogencarbonate, sold as baking soda and used to make cakes rise when it releases carbon dioxide on heating or on reaction with an acid. Washing soda is Na2CO3·10H2O, caustic soda is NaOH and bleaching powder is CaOCl2. Matching the formula to the name is the reliable way to answer.

Question 29Chemical Substances and Processes

A sample of hard water does not lather readily with soap. Which ion is chiefly responsible for this behaviour?

  1. Calcium ion Correct answer.
  2. Chloride ion
  3. Sodium ion
  4. Nitrate ion

Explanation

Hard water contains dissolved calcium and magnesium ions, which react with soap to form an insoluble scum instead of lather. Sodium, chloride and nitrate ions do not form such precipitates with soap, so they do not cause hardness. This is why hard water wastes soap and is softened before use in laundries.

Question 30Chemical Substances and Processes

Which property of a metal makes it suitable for making thin wires for electrical transmission?

  1. Low cost only
  2. Ductility with good electrical conductivity Correct answer.
  3. High melting point
  4. High density

Explanation

Electrical wiring needs a metal that conducts current well and can be drawn into long thin wires without breaking, which is ductility. Copper and aluminium combine both properties, so they dominate transmission cables. Melting point, density and price matter for some uses but do not by themselves explain the wire-drawing requirement.

Question 31Chemical Substances and Processes

A student adds a few drops of universal indicator to a solution and it turns green. What does this show about the solution?

  1. It is weakly acidic.
  2. It is strongly acidic.
  3. It is neutral. Correct answer.
  4. It is strongly basic.

Explanation

Universal indicator gives a green colour at pH 7, which is the neutral point. Red to orange shades indicate strong acidity, yellow-green indicates weak acidity, and blue to violet indicates basicity. The single colour therefore places the solution at neutrality.

Question 32Chemical Substances and Processes

Why is sodium stored under kerosene oil in the laboratory?

  1. To increase its reactivity before use
  2. To prevent it from reacting with moisture and oxygen in air Correct answer.
  3. To keep it cool during storage
  4. To dissolve impurities from its surface

Explanation

Sodium is so reactive that it catches fire on contact with atmospheric moisture and oxygen, forming sodium hydroxide and hydrogen. Kerosene is an inert liquid that excludes air and moisture, so the metal stays unreacted. It is not a coolant, an activator or a purifying agent.

Question 33Chemical Substances and Processes

Which of the following statements about the reaction between dilute nitric acid and sodium carbonate is correct?

  1. Carbon dioxide is evolved and sodium nitrate is formed. Correct answer.
  2. Hydrogen is evolved and sodium nitrate is formed.
  3. Oxygen is evolved and sodium hydroxide is formed.
  4. No gas is evolved because nitric acid is a weak acid.

Explanation

Acids react with carbonates to give a salt, carbon dioxide and water: Na2CO3 + 2HNO3 → 2NaNO3 + H2O + CO2. The salt here is sodium nitrate because the acid supplies the nitrate ion. The carbon dioxide turns limewater milky, which confirms the reaction.

Question 34Chemical Substances and Processes

In the reaction 2Pb(NO3)2 → 2PbO + 4NO2 + O2, which type of reaction is shown?

  1. Neutralisation reaction
  2. Displacement reaction
  3. Combination reaction
  4. Thermal decomposition reaction Correct answer.

Explanation

A single compound, lead(II) nitrate, breaks down on heating into three simpler substances, so this is thermal decomposition. The brown fumes of nitrogen dioxide are the familiar sign of this reaction. Combination, neutralisation and displacement all require two or more reactants or a more reactive element taking the place of another.

Question 35Chemical Substances and Processes

A metal M reacts with dilute hydrochloric acid but not with cold water, and it displaces copper from copper sulphate solution. Where is M most likely placed in the reactivity series?

  1. Below copper but above silver
  2. Above potassium
  3. Below silver but above copper Correct answer.
  4. Below gold

Explanation

Reaction with dilute acid shows M lies above hydrogen, while no reaction with cold water shows it lies below the very reactive metals such as potassium and sodium. Displacing copper places it above copper in the series. Combining these clues puts M between hydrogen and the highly reactive metals, so above copper but below potassium.

Question 36Chemical Substances and Processes

Aqueous solutions of sodium chloride, hydrochloric acid and glucose are tested with a conductivity tester. Which statement correctly compares their electrical conductivity?

  1. Sodium chloride and hydrochloric acid conduct electricity because they furnish ions in solution, while glucose does not. Correct answer.
  2. All three solutions conduct electricity because each solute dissolves in water to give free electrons.
  3. Only glucose conducts electricity because it is a covalent compound that ionises completely in water.
  4. Sodium chloride conducts electricity, but hydrochloric acid and glucose do not because neither forms ions in water.

Explanation

Conduction in solution requires mobile ions. Sodium chloride is an ionic solid that dissociates into Na+ and Cl- ions, and hydrochloric acid ionises in water to give H+ and Cl- ions, so both solutions conduct. Glucose is a covalent molecular compound that dissolves without forming ions, so its solution does not conduct.

Question 37World of Living

Which cell organelle is described as the powerhouse of the cell because it releases energy through cellular respiration?

  1. Ribosome
  2. Lysosome
  3. Golgi apparatus
  4. Mitochondrion Correct answer.

Explanation

The mitochondrion carries out aerobic respiration, oxidising pyruvate from glucose to release energy stored as ATP, so it is called the powerhouse of the cell. Ribosomes build proteins, the Golgi apparatus packages and modifies secretions, and lysosomes digest waste, none of which is the cell's main energy-releasing site.

Question 38World of Living

A student observes a peel of onion under the microscope. Which structure is clearly visible as the outermost boundary of each cell and gives the cell a fixed shape?

  1. Plasma membrane
  2. Nuclear membrane
  3. Cell wall Correct answer.
  4. Tonoplast

Explanation

Plant cells like onion peel have a rigid cellulose cell wall outside the plasma membrane, and this wall maintains the fixed polygonal shape seen under the microscope. The plasma membrane lies just inside it and is too thin to be the prominent outer boundary, while the nuclear membrane and tonoplast are internal membranes.

Question 39World of Living

Which tissue in a plant conducts water and dissolved minerals upward from the roots to the leaves?

  1. Cambium
  2. Xylem Correct answer.
  3. Epidermis
  4. Phloem

Explanation

Xylem is the conducting tissue that carries water and mineral salts unidirectionally from roots to leaves through tracheids and vessels. Phloem transports prepared food in both directions, cambium is a meristem that produces new vascular tissue, and epidermis is a protective outer layer.

Question 40World of Living

In which part of the human alimentary canal is most of the digestion of starch completed and absorption of glucose begun?

  1. Small intestine Correct answer.
  2. Large intestine
  3. Stomach
  4. Oesophagus

Explanation

The small intestine receives pancreatic amylase and its own enzymes, completing starch digestion to glucose, and its villi absorb the glucose into the blood. The stomach mainly digests proteins, the large intestine absorbs water and salts, and the oesophagus only conducts food by peristalsis.

Question 41World of Living

Which of the following is a characteristic feature of living organisms that a burning candle does not show?

  1. Growth from inside by cell division Correct answer.
  2. Consumption of oxygen
  3. Production of light
  4. Release of heat energy

Explanation

Living organisms grow from within by division and enlargement of their own cells, which a candle cannot do. A burning candle does use oxygen, gives out heat and light, and these are non-living processes that resemble some life activities but lack cellular growth and organisation.

Question 42World of Living

Which process allows a single-celled Amoeba to produce two daughter cells without the formation of gametes?

  1. Spore formation
  2. Budding
  3. Binary fission Correct answer.
  4. Fragmentation

Explanation

Amoeba reproduces asexually by binary fission, in which the nucleus divides first and the cytoplasm then splits into two equal daughter cells. Budding occurs in yeast, fragmentation in multicellular forms like Spirogyra, and spore formation in Rhizopus, none of which describes Amoeba.

Question 43World of Living

Which part of the human female reproductive system is the normal site of fertilisation of the ovum by a sperm?

  1. Fallopian tube Correct answer.
  2. Ovary
  3. Uterus
  4. Vagina

Explanation

Fertilisation usually occurs in the fallopian tube, where the sperm meets the ovum as it travels towards the uterus. The ovary releases the ovum, the uterus receives and nourishes the embryo after implantation, and the vagina is the birth canal, so none of these is the fusion site.

Question 44World of Living

Which of the following is an example of an acquired trait in humans?

  1. Colour of the eyes
  2. Type of earlobe
  3. Body weight gained through diet Correct answer.
  4. Ability to roll the tongue

Explanation

Acquired traits develop during a lifetime in response to the environment or habits and are not passed to offspring; body weight gained through diet is such a trait. Eye colour, tongue rolling and earlobe type are inherited traits determined by genes.

Question 45World of Living

A pea plant heterozygous for plant height (Tt) is crossed with a dwarf pea plant (tt). What proportion of the offspring is expected to be dwarf?

  1. One half Correct answer.
  2. Three fourths
  3. All offspring
  4. One fourth

Explanation

The cross Tt x tt gives gametes T and t from the tall parent and only t from the dwarf parent, producing Tt and tt in equal numbers. Thus half the offspring are tall heterozygotes and half are dwarf, so one half is the correct proportion.

Question 46World of Living

Two parents with blood group A and blood group B have a child with blood group O. Which genotype combination of the parents explains this?

  1. IAi and IBi Correct answer.
  2. IAIA and IBi
  3. IAi and IBIB
  4. IAIA and IBIB

Explanation

Blood group O requires the genotype ii, so each parent must contribute an i allele. Both parents must therefore carry one i allele, giving the genotypes IAi and IBi, which also express groups A and B respectively.

Question 47World of Living

In a food chain, grass is eaten by a grasshopper, which is eaten by a frog, which is eaten by a snake. Which trophic level does the frog occupy?

  1. Secondary consumer Correct answer.
  2. Primary consumer
  3. Tertiary consumer
  4. Producer

Explanation

Grass is the producer, the grasshopper is the primary consumer that eats it, and the frog that eats the grasshopper is the secondary consumer. The snake, feeding on the frog, occupies the tertiary consumer level.

Question 48World of Living

Which human activity is most directly responsible for the process of biological magnification of pesticides in a pond ecosystem?

  1. Rainwater harvesting near the pond
  2. Planting trees around the pond
  3. Spraying of pesticides on crops near the pond Correct answer.
  4. Use of biogas for cooking

Explanation

Pesticides sprayed on fields are washed into water bodies, where they enter the food chain and increase in concentration at each trophic level, a process called biological magnification. Planting trees, rainwater harvesting and biogas use do not add persistent pesticides to the food chain.

Question 49World of Living

Which of the following best explains why the ozone layer is important for living organisms?

  1. It absorbs most ultraviolet radiation from the sun. Correct answer.
  2. It supplies oxygen for respiration.
  3. It reflects radio waves back to the ground.
  4. It traps infrared radiation and warms the earth.

Explanation

The ozone layer in the stratosphere absorbs most of the harmful ultraviolet radiation from the sun, protecting organisms from skin damage and mutation. It does not act as the main greenhouse gas, supply oxygen for respiration, or reflect radio waves.

Question 50World of Living

A student keeps a potted plant in a dark cupboard for three days and then tests a leaf with iodine solution. What result is expected and why?

  1. Blue-black colour, because respiration produces starch in the dark
  2. No colour change, because iodine does not react with leaf tissue
  3. No blue-black colour, because photosynthesis cannot occur without light Correct answer.
  4. Blue-black colour, because starch is still being made in the dark

Explanation

Photosynthesis needs light to produce glucose, which is stored as starch, so a plant kept in darkness uses up its starch and cannot make more. The iodine test therefore shows no blue-black colour in the leaf.