Ch 1Chemical Reactions and Equations
2-Mark Questions
Why should a magnesium ribbon be cleaned before burning in air?
Magnesium reacts with the oxygen of the air to form a thin layer of magnesium oxide (MgO) on its surface. This oxide layer is unreactive and prevents the ribbon from burning properly. Therefore the ribbon is cleaned with sandpaper to remove the oxide layer, so that the clean magnesium can burn easily in air with a bright white flame.
Write the balanced equation for the following chemical reactions. (i) Hydrogen + Chlorine → Hydrogen chloride (ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride (iii) Sodium + Water → Sodium hydroxide + Hydrogen
(i) H₂ + Cl₂ → 2HCl (ii) 3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃ (iii) 2Na + 2H₂O → 2NaOH + H₂
Write a balanced chemical equation with state symbols for the following reactions. (i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
(i) BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq) (ii) NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
1-Mark Questions (MCQ)
Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO₂(g) (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced.
(i) (a) and (b)
Ch 2Acids, Bases and Salts
2-Mark Questions
Why should curd and sour substances not be kept in brass and copper vessels?
Curd and sour foods contain acids. Acids react with copper and brass to form soluble metal salts, which can make the food poisonous and unfit to eat. Therefore such substances should not be kept in copper or brass vessels.
Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Hydrogen gas is usually liberated. For example, zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen: Zn + H₂SO₄ → ZnSO₄ + H₂. The gas is tested by bringing a burning candle near it; hydrogen burns with a pop sound.
Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
The gas is carbon dioxide, so compound A is calcium carbonate. The balanced equation is: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O. Carbon dioxide extinguishes a burning candle.
1-Mark Questions (MCQ)
A solution turns red litmus blue, its pH is likely to be
(d) 10
Ch 3Metals and Non-metals
2-Mark Questions
Give an example of a metal which (i) is a liquid at room temperature. (ii) can be easily cut with a knife. (iii) is the best conductor of heat. (iv) is a poor conductor of heat.
(i) Mercury is liquid at room temperature. (ii) Sodium can be easily cut with a knife. (iii) Silver is the best conductor of heat. (iv) Lead is a poor conductor of heat.
Explain the meanings of malleable and ductile.
Malleable means a substance can be beaten into thin sheets. Ductile means it can be drawn into thin wires. Metals generally show both these properties.
Why is sodium kept immersed in kerosene oil?
Sodium is very reactive and reacts vigorously with oxygen and moisture in air, producing heat and possibly catching fire. It is kept under kerosene oil to prevent contact with air and water.
1-Mark Questions (MCQ)
Which of the following pairs will give displacement reactions?
(d) AgNO₃ solution and copper metal.
Ch 4Carbon and its Compounds
2-Mark Questions
What would be the electron dot structure of carbon dioxide which has the formula CO₂?
Carbon dioxide has two double covalent bonds. Its electron-dot structure is O=C=O, with carbon sharing two pairs of electrons with each oxygen atom; each oxygen also has two lone pairs.
What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)
A sulphur molecule is S₈. The eight sulphur atoms are joined in a ring by single covalent bonds; each sulphur shares one electron with each of two neighbouring sulphur atoms and has two lone pairs remaining.
How many structural isomers can you draw for pentane?
Three structural isomers can be drawn for pentane: n-pentane, isopentane (2-methylbutane) and neopentane (2,2-dimethylpropane).
1-Mark Questions (MCQ)
Ethane, with the molecular formula C₂H₆ has
(b) 7 covalent bonds.
Ch 5Life Processes
2-Mark Questions
Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?
In multicellular organisms, all cells are not in direct contact with the external environment. Diffusion is too slow to transport oxygen over long distances and cannot meet the high oxygen demand of many cells, so specialised transport and respiratory systems are needed.
What criteria do we use to decide whether something is alive?
We look for life processes such as nutrition, respiration, transport, excretion, growth, response to stimuli and reproduction. Even when visible movement is absent, molecular movement and maintenance processes continue in living organisms.
What are outside raw materials used for by an organism?
Outside raw materials are used to build the body, repair tissues and release energy. They include food as a source of carbon and energy, oxygen for respiration, and water and minerals for biochemical processes.
1-Mark Questions (MCQ)
The kidneys in human beings are a part of the system for
(c) excretion.
Ch 6Control and Coordination
2-Mark Questions
What is the difference between a reflex action and walking?
A reflex action is a quick, automatic and involuntary response to a stimulus, usually through a reflex arc. Walking is a voluntary activity controlled by the brain, though it involves coordinated muscle action and balance.
What happens at the synapse between two neurons?
At a synapse, the electrical impulse at the end of one neuron causes release of chemical neurotransmitters. These chemicals cross the synaptic gap and start a new electrical impulse in the next neuron.
Which part of the brain maintains posture and equilibrium of the body?
The cerebellum, a part of the hindbrain, maintains posture and equilibrium of the body.
1-Mark Questions (MCQ)
Which of the following is a plant hormone?
(d) Cytokinin.
Ch 7How do Organisms Reproduce?
2-Mark Questions
What is the importance of DNA copying in reproduction?
DNA copying passes genetic information from parents to offspring. It also produces small variations during copying, and these variations help populations adapt and survive in changing environments.
Why is variation beneficial to the species but not necessarily for the individual?
Variation may or may not help a particular individual survive. But in a species, variations create diversity, so if the environment changes, some individuals may be better adapted and the species can survive.
How does binary fission differ from multiple fission?
In binary fission, one parent cell divides into two daughter cells, as in Amoeba. In multiple fission, one parent cell divides simultaneously into many daughter cells, as in Plasmodium.
1-Mark Questions (MCQ)
Asexual reproduction takes place through budding in
(b) Yeast.
Ch 8Heredity
2-Mark Questions
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Trait B is likely to have arisen earlier. In an asexually reproducing population, a trait present in a larger fraction of individuals has probably had more time to spread through reproduction.
How does the creation of variations in a species promote survival?
Variations create differences among individuals. If environmental conditions change, some variations may give certain individuals a survival advantage, allowing them to reproduce and helping the species continue.
How do Mendel's experiments show that traits may be dominant or recessive?
Mendel crossed pure tall pea plants with pure short pea plants. All F₁ plants were tall, showing that tallness was dominant over shortness. When F₁ plants self-pollinated, short plants reappeared in F₂, showing that the short trait was present but recessive.
1-Mark Questions (MCQ)
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
(c) TtWW
Ch 9Light – Reflection and Refraction
2-Mark Questions
Define the principal focus of a concave mirror.
The principal focus of a concave mirror is the point on its principal axis where rays parallel to the principal axis meet after reflection from the mirror.
The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
The focal length is 10 cm.
Name a mirror that can give an erect and enlarged image of an object.
A concave mirror can give an erect and enlarged image when the object is placed between the pole and the principal focus.
1-Mark Questions (MCQ)
Which one of the following materials cannot be used to make a lens?
(d) Clay
Ch 10The Human Eye and the Colourful World
2-Mark Questions
What is meant by power of accommodation of the eye?
Power of accommodation is the ability of the eye lens to adjust its focal length so that objects at different distances are focused clearly on the retina.
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
A concave, or diverging, lens should be used. It diverges light from distant objects so that the image is formed on the retina of the myopic eye.
What is the far point and near point of the human eye with normal vision?
For a normal human eye, the far point is infinity and the near point is about 25 cm from the eye.
1-Mark Questions (MCQ)
The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due to
(b) accommodation.
Ch 11Electricity
2-Mark Questions
What does an electric circuit mean?
An electric circuit is a continuous and closed conducting path through which electric current flows. It usually includes a source such as a cell or battery, connecting wires and circuit components.
Define the unit of current.
The SI unit of current is the ampere. One ampere is the current flowing when one coulomb of charge passes through a conductor in one second: 1 A = 1 C s⁻¹.
Calculate the number of electrons constituting one coulomb of charge.
One coulomb of charge contains about 6.25 × 10¹⁸ electrons.
1-Mark Questions (MCQ)
A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R', then the ratio R/R' is –
(d) 25
Ch 12Magnetic Effects of Electric Current
2-Mark Questions
Draw magnetic field lines around a bar magnet.
Magnetic field lines around a bar magnet form closed curves. Outside the magnet they emerge from the north pole and enter the south pole; inside the magnet they go from south pole to north pole. The lines are crowded near the poles where the magnetic field is strongest.
List the properties of magnetic field lines.
Magnetic field lines are closed continuous curves. Outside a magnet they go from north pole to south pole, and inside the magnet from south pole to north pole. The tangent at any point gives the direction of the magnetic field. The closer the lines, the stronger the field. No two magnetic field lines intersect.
Why don't two magnetic field lines intersect each other?
If two magnetic field lines intersected, the magnetic field at the point of intersection would have two directions, which is impossible. Therefore magnetic field lines never intersect.
1-Mark Questions (MCQ)
Choose the correct option. The magnetic field inside a long straight solenoid-carrying current
(d) is the same at all points.
Ch 13Our Environment
2-Mark Questions
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Trophic levels are the feeding levels in a food chain. Example: grass → deer → lion. Grass is the producer and first trophic level, deer is the primary consumer and second trophic level, and lion is the secondary consumer and third trophic level.
What is the role of decomposers in the ecosystem?
Decomposers break down dead plants, animals and organic wastes into simpler substances. They recycle nutrients back into the soil and help maintain the flow of matter in the ecosystem.
Why are some substances biodegradable and some non-biodegradable?
Substances are biodegradable if decomposers such as bacteria and fungi can break them down using biological processes. Some substances are non-biodegradable because their chemical structure cannot be easily broken down by decomposers, or breaks down extremely slowly.
1-Mark Questions (MCQ)
Which of the following groups contain only biodegradable items?
(a), (c) and (d)
Frequently asked questions
- Why should a magnesium ribbon be cleaned before burning in air?
- Magnesium reacts with the oxygen of the air to form a thin layer of magnesium oxide (MgO) on its surface. This oxide layer is unreactive and prevents the ribbon from burning properly. Therefore the ribbon is cleaned with sandpaper to remove the oxide layer, so that the clean magnesium can burn easily in air with a bright white flame.
- Write the balanced equation for the following chemical reactions. (i) Hydrogen + Chlorine → Hydrogen chloride (ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride (iii) Sodium + Water → Sodium hydroxide + Hydrogen
- (i) H₂ + Cl₂ → 2HCl (ii) 3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃ (iii) 2Na + 2H₂O → 2NaOH + H₂
- Write a balanced chemical equation with state symbols for the following reactions. (i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
- (i) BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq) (ii) NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
- Why should curd and sour substances not be kept in brass and copper vessels?
- Curd and sour foods contain acids. Acids react with copper and brass to form soluble metal salts, which can make the food poisonous and unfit to eat. Therefore such substances should not be kept in copper or brass vessels.
These important questions are selected from the NCERT Class 10 Science textbook book-back exercises to help you revise the most useful questions. Mark weightage (5/2/1) follows the usual exam pattern and may vary by exam — always check your latest syllabus and question pattern. Open each chapter for the complete set of questions and answers.