BSEB · Matric (Class 10) · 2022 – 2026
Bihar Board Class 10 Science
Previous Year Questions with Solutions — Chapter-wise
Built by reading 9 official BSEB question papers from 2022 to 2026 — sets A, D, E, F, G, I and J.
240 solved questions · 16 chapters · 15 in each · repeated questions carry a 4× chip showing how many of the 9 papers they appeared in
Chapter 1 · ChemistryChemical Reactions and Equations
15 solved questions · 3 of them repeated across papers
What is a balanced chemical equation? Give an example. Why is it necessary to balance a chemical equation?
A balanced chemical equation is one in which the number of atoms of each element is equal on both sides of the equation.
Example:
Zn + H2SO4 → ZnSO4 + H2↑Why balancing is necessary: because of the law of conservation of mass, which says that matter can neither be created nor destroyed in a chemical reaction. The total mass of the reactants must equal the total mass of the products, so the atoms on both sides must match.
An unbalanced equation would mean atoms had appeared from nowhere or vanished, which is impossible.
Only the coefficients in front of a formula may be changed while balancing. Changing a subscript turns the substance into a different one altogether.
Write three pieces of information obtained from a chemical equation.
Taking the equation:
2Mg + O2 ⟶burn 2MgO- The reactants and the products. Magnesium and oxygen react, and magnesium oxide is formed.
- The number of atoms and molecules taking part. Two atoms of magnesium react with one molecule of oxygen to give two units of magnesium oxide.
- The physical states and conditions. Symbols such as (s), (l), (g), (aq) show the state, and words written above the arrow show the conditions — heat, sunlight, a catalyst, or pressure.
A chemical equation also shows whether a gas is evolved (↑) or a precipitate is formed (↓), and whether the reaction is exothermic or endothermic when the heat term is written.
The reaction in which heat is evolved along with the formation of products is called:
- (A) Endothermic reaction
- (B) Exothermic reaction
- (C) Displacement reaction
- (D) Decomposition reaction
(B) Exothermic reaction
CaO + H2O → Ca(OH)2 + heat| Exothermic | Endothermic | |
|---|---|---|
| Heat | Released | Absorbed |
| Surroundings become | Warm | Cold |
| Examples | Burning of fuels, respiration, quick lime + water | Decomposition of CaCO3, photosynthesis |
Respiration is exothermic — a related MCQ from the 2022 paper. Glucose is broken down and energy is released, which is how our body stays warm.
The reaction in which ions are exchanged between two compounds is called:
- (A) displacement
- (B) double displacement
- (C) combination
- (D) precipitation
(B) Double displacement
Na2SO4 + BaCl2 → BaSO4↓ + 2NaClThe two compounds swap their ions — barium joins the sulphate, sodium joins the chloride.
Why not (D): precipitation describes the result — that an insoluble solid appears. Not every double displacement gives a precipitate; neutralisation is a double displacement that gives only salt and water. So double displacement is the more accurate name for the exchange itself.
Tell the two apart by counting reactants: in displacement, one free element pushes another out of its compound. In double displacement, two compounds exchange partners.
The reactions that take place by the absorption of sunlight are called:
- (A) Combination reaction
- (B) Photo-chemical reaction
- (C) Redox reaction
- (D) Displacement reaction
(B) Photo-chemical reaction
2AgCl ⟶sunlight 2Ag + Cl2White silver chloride turns grey in sunlight, because silver metal is set free.
2AgBr ⟶sunlight 2Ag + Br2Use: both reactions are used in black-and-white photography.
Such reactions are also decomposition reactions, and since light energy is absorbed, they are endothermic.
The addition of oxygen to a substance during a chemical reaction is called:
- (A) Reduction
- (B) Oxidation
- (C) Corrosion
- (D) Rancidity
(B) Oxidation
| Oxidation | Reduction | |
|---|---|---|
| Oxygen | Gained | Lost |
| Hydrogen | Lost | Gained |
Copper gains oxygen, so it is oxidised. The shiny brown copper turns black.
A redox reaction is one in which both happen together:
CuO + H2 → Cu + H2OHere CuO is reduced and H2 is oxidised in the same reaction.
What is corrosion? Explain with an example and write two methods of preventing it.
Corrosion is the gradual eating away of the surface of a metal by the action of air, moisture or chemicals around it.
Example — rusting of iron: a reddish-brown layer of hydrated iron oxide forms.
4Fe + 3O2 + xH2O → 2Fe2O3·xH2OOther examples: silver turns black on exposure to air, and copper develops a green coating of basic copper carbonate.
Two methods of prevention:
- Painting, oiling or greasing, which keeps air and moisture away from the surface.
- Galvanisation — coating iron with zinc, which being more reactive corrodes in place of the iron.
Rusting needs both air and water. Iron does not rust in dry air, nor in boiled water sealed under oil — which is the standard three-test-tube experiment.
Describe a precipitation reaction with an example.
A reaction in which an insoluble solid is formed on mixing two solutions is a precipitation reaction, and the solid is called the precipitate.
Pb(NO3)2 + 2KI → PbI2↓ + 2KNO3On mixing the two colourless solutions, a bright yellow precipitate of lead iodide appears immediately.
Another example:
BaCl2 + Na2SO4 → BaSO4↓ + 2NaClHere the precipitate of barium sulphate is white.
Every precipitation reaction is also a double displacement reaction, since the two compounds exchange ions.
An element combines with oxygen to form an oxide. This reaction is:
- (A) Decomposition
- (B) Combination
- (C) Double displacement
- (D) Precipitation
(B) Combination reaction
In a combination reaction two or more substances join to form a single product.
2Mg + O2 → 2MgO C + O2 → CO2Because oxygen is being added, the reaction is also an oxidation. Most combination reactions with oxygen are exothermic as well — magnesium burns with a dazzling white flame.
Remember the shape of each type: combination is many → one, decomposition is one → many. Counting the reactants and products usually settles the answer.
What is liberated by the complete oxidation of glucose in the body?
- (A) Only CO2
- (B) Only energy
- (C) CO2, water and energy
- (D) Only water
(C) Carbon dioxide, water and energy
C6H12O6 + 6O2 → 6CO2 + 6H2O + energyThis is aerobic respiration — a slow, controlled combustion of glucose inside our cells, taking place in the mitochondria.
Why it is called an oxidation: glucose combines with oxygen, so it is oxidised. Since energy is released, respiration is an exothermic reaction — and this is where our body heat comes from.
Write the balanced chemical equations for the following reactions:
- (i) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
- (ii) Zinc + Silver nitrate → Zinc nitrate + Silver
- (iii) Aluminium + Copper chloride → Aluminium chloride + Copper
(i)
Ca(OH)2 + CO2 → CaCO3↓ + H2OThis is the lime water test for carbon dioxide — the solution turns milky.
(ii)
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag(iii)
2Al + 3CuCl2 → 2AlCl3 + 3CuBoth (ii) and (iii) are displacement reactions — the more reactive metal pushes out the less reactive one.
A quick method: balance the metal first, then the non-metal, and leave hydrogen and oxygen for the end, since they usually appear in the most places.
What are oxidation–reduction reactions? Identify the oxidising and reducing agents in the reaction below.
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2A reaction in which oxidation and reduction take place at the same time is called a redox reaction.
| Substance | What happens | It is | Its role |
|---|---|---|---|
| MnO2 | Loses oxygen | Reduced | Oxidising agent |
| HCl | Loses hydrogen | Oxidised | Reducing agent |
The rule in one line: the substance that is reduced is the oxidising agent, and the one that is oxidised is the reducing agent. The agent is always the opposite of what happens to it.
This is the single most common slip in the chapter — writing that the oxidised substance is the oxidising agent. Read the table above once more before the exam.
What is rancidity? Write two methods of preventing it.
Rancidity is the change that takes place when the fats and oils in food are oxidised on standing in air, so that the food develops an unpleasant smell and taste.
Two methods of prevention:
- Adding antioxidants, which get oxidised in place of the fat and so delay rancidity.
- Packing the food in nitrogen, an unreactive gas, so that no oxygen is present — this is why chip packets are puffed up with nitrogen.
Other ways: keeping food in airtight containers, refrigerating it, and keeping it away from light.
Since rancidity is an oxidation, every one of these works by keeping oxygen away or slowing the reaction down.
When a magnesium ribbon is burnt in air, the product formed is:
- (A) Magnesium hydroxide
- (B) Magnesium oxide
- (C) Magnesium carbonate
- (D) Magnesium nitride only
(B) Magnesium oxide
2Mg + O2 ⟶burn 2MgOWhat you observe: the ribbon burns with a dazzling white flame and leaves behind a white powder of magnesium oxide.
Why the ribbon is cleaned first: magnesium reacts with the moisture and oxygen of the air, so a layer…