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📘 Study MCQs
Q1. What is a chemical equation?
A. A statement of physical change
B. A representation of a chemical reaction
C. A mathematical formula
D. A physical law
B. A representation of a chemical reaction
A chemical equation uses symbols and formulas to show the substances that undergo change (reactants) and the new substances formed (products) during a chemical reaction.
Q2. The substances that take part in a chemical reaction are called:
A. Products
B. Reactants
C. Elements
D. Compounds
B. Reactants
Reactants are the starting materials in a chemical reaction that are consumed to form new substances.
Q3. The substances formed after a chemical reaction are called:
A. Reactants
B. Residues
C. Products
D. Mixtures
C. Products
Products are the substances that are formed as a result of a chemical reaction, appearing on the right side of a chemical equation.
Q4. Which symbol separates reactants and products in a chemical equation?
A. +
B. →
C. ×
B. →
The arrow (→) is read as “yields,” “produces,” or “gives,” and it separates the reactants from the products in a chemical equation.
Q5. What does the plus sign (+) indicate in a chemical equation?
A. Gives
B. Equals
C. And
D. Heat
C. And
The plus sign is used to separate two or more reactants or two or more products, indicating that they are combined or formed together.
Q6. Which of the following is a chemical change?
A. Melting ice
B. Boiling water
C. Rusting iron
D. Cutting paper
C. Rusting iron
Rusting is a chemical change because iron reacts with oxygen to form a new substance (iron oxide), unlike physical changes which alter only the state or form.
Q7. A chemical equation written in words is called:
A. Balanced equation
B. Word equation
C. Skeletal equation
D. Symbolic equation
B. Word equation
A word equation uses the names of reactants and products to describe a chemical reaction, e.g., Hydrogen + Oxygen → Water.
Q8. Which law is used to balance chemical equations?
A. Law of gravity
B. Law of conservation of mass
C. Law of motion
D. Law of energy
B. Law of conservation of mass
This law states that matter cannot be created or destroyed, so the number of atoms of each element must be the same on both sides of a chemical equation.
Q9. In a balanced chemical equation, the number of atoms on both sides is:
A. Different
B. Unequal
C. Same
D. Random
C. Same
Balancing an equation ensures that the number of atoms for each element is equal on the reactant and product sides, satisfying the law of conservation of mass.
Q10. Which of the following is a word equation?
A. H₂ + O₂ → H₂O
B. Hydrogen + Oxygen → Water
C. 2H₂ + O₂ → 2H₂O
D. H₂O → H₂ + O₂
B. Hydrogen + Oxygen → Water
A word equation uses the full names of elements and compounds rather than their chemical symbols.
Q11. What does the symbol (s) indicate?
A. Solid
B. Solution
C. Gas
D. Liquid
A. Solid
The symbol (s) is a state symbol placed after a chemical formula to indicate that the substance is in a solid state.
Q12. The symbol (l) represents:
A. Liquid
B. Light
C. Layer
D. Lime
A. Liquid
The symbol (l) is a state symbol that indicates the substance is in a liquid state.
Q13. Which symbol shows gaseous state?
A. (s)
B. (l)
C. (aq)
D. (g)
D. (g)
The symbol (g) is placed after a chemical formula to indicate that the substance is a gas.
Q14. The symbol (aq) means:
A. Solid
B. Liquid
C. Gas
D. Dissolved in water
D. Dissolved in water
(aq) stands for aqueous, meaning the substance is dissolved in water to form a solution.
Q15. A skeletal equation is:
A. Balanced equation
B. Unbalanced equation
C. Word equation
D. Nuclear equation
B. Unbalanced equation
A skeletal equation uses correct chemical formulas but does not have coefficients to balance the number of atoms on both sides.
Q16. Which of the following must be true for a balanced equation?
A. Same number of molecules
B. Same mass on both sides
C. Same volume
D. Same colour
B. Same mass on both sides
According to the law of conservation of mass, the total mass of reactants must equal the total mass of products in a balanced chemical equation.
Q17. Which side of a chemical equation contains reactants?
A. Right side
B. Left side
C. Below arrow
D. Above arrow
B. Left side
By convention, reactants are written on the left side of the arrow in a chemical equation.
Q18. Products are written on which side of the equation?
A. Left side
B. Below arrow
C. Right side
D. Above arrow
C. Right side
Products are written on the right side of the arrow in a chemical equation.
Q19. What does the arrow (→) mean?
A. Equals
B. Plus
C. Gives
D. Heat
C. Gives
The arrow is read as “yields,” “produces,” or “gives,” indicating the direction of the reaction from reactants to products.
Q20. Which of the following shows a chemical reaction?
A. Breaking glass
B. Melting wax
C. Burning coal
D. Freezing water
C. Burning coal
Burning coal is a chemical reaction (combustion) where coal reacts with oxygen to form new substances like carbon dioxide and ash.
Q21. Which of the following is NOT shown by a chemical equation?
A. Reactants
B. Products
C. Mass balance
D. Speed of reaction
D. Speed of reaction
A chemical equation provides qualitative information about reactants and products, but it does not indicate the rate or speed at which the reaction occurs.
Q22. Why are coefficients used in chemical equations?
A. To change formulas
B. To balance equations
C. To add substances
D. To remove atoms
B. To balance equations
Coefficients are numbers placed before chemical formulas to multiply the entire compound, ensuring the number of atoms for each element is equal on both sides.
Q23. In H₂ + O₂ → H₂O, H₂ and O₂ are:
A. Products
B. Reactants
C. Catalysts
D. Residues
B. Reactants
H₂ and O₂ appear on the left side of the arrow, so they are the starting substances or reactants in this reaction.
Q24. In the reaction Mg + O₂ → MgO, MgO is a:
A. Reactant
B. Element
C. Product
D. Mixture
C. Product
MgO appears on the right side of the arrow, so it is the substance formed as a product of the reaction.
Q25. What type of change is represented by a chemical equation?
A. Physical change
B. Chemical change
C. Temporary change
D. Reversible change
B. Chemical change
A chemical equation represents a chemical change, where substances react to form new substances with different properties.
Q26. Which of the following obeys the law of conservation of mass?
A. Word equation
B. Skeletal equation
C. Balanced equation
D. Unbalanced equation
C. Balanced equation
Only a balanced equation has the same number of atoms of each element on both sides, thus obeying the law of conservation of mass.
Q27. What happens to atoms during a chemical reaction?
A. They are destroyed
B. They are created
C. They are rearranged
D. They disappear
C. They are rearranged
Atoms are neither created nor destroyed in a chemical reaction; they are simply rearranged to form new substances.
Q28. Which symbol is used to show heat?
A. +
B. Δ
C. →
B. Δ
The Greek letter delta (Δ) written above or below the arrow indicates that heat is supplied to the reaction.
Q29. A chemical equation is balanced by changing:
A. Chemical formulas
B. Number of atoms
C. Coefficients
D. Symbols
C. Coefficients
Balancing involves placing coefficients in front of formulas; the chemical formulas themselves cannot be changed as they represent the actual substances.
Q30. Which of the following is a balanced equation?
A. H₂ + O₂ → H₂O
B. 2H₂ + O₂ → 2H₂O
C. H₂ + O → H₂O
D. H + O₂ → H₂O
B. 2H₂ + O₂ → 2H₂O
This equation has 4 hydrogen atoms and 2 oxygen atoms on both the reactant and product sides, making it balanced.
Q31. Chemical equations are useful because they:
A. Show reactions clearly
B. Increase weight
C. Change colour
D. Slow reactions
A. Show reactions clearly
Chemical equations provide a concise and clear way to represent what happens during a chemical reaction.
Q32. Which of the following is a reactant?
A. Substance formed
B. Starting substance
C. Final product
D. Residue
B. Starting substance
Reactants are the substances that are present at the start of a chemical reaction.
Q33. Which one is a chemical formula?
A. Water
B. Liquid
C. H₂O
D. Solid
C. H₂O
A chemical formula uses element symbols and subscripts to represent the composition of a substance.
Q34. What is the formula of carbon dioxide?
A. CO
B. CO₂
C. C₂O
D. CO₃
B. CO₂
Carbon dioxide consists of one carbon atom and two oxygen atoms, hence the formula CO₂.
Q35. Which change forms a new substance?
A. Boiling water
B. Melting ice
C. Rusting iron
D. Freezing milk
C. Rusting iron
Rusting produces iron oxide, a new substance with different properties from iron and oxygen.
Q36. What is always conserved in a chemical reaction?
A. Volume
B. Mass
C. Colour
D. Shape
B. Mass
The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction.
Q37. Which part of the equation shows physical states?
A. Coefficients
B. Symbols
C. State symbols
D. Arrow
C. State symbols
State symbols such as (s), (l), (g), and (aq) indicate the physical state of each substance in the reaction.
Q38. A chemical equation does NOT show:
A. Reactants
B. Products
C. Energy change
D. Colour change
D. Colour change
While a chemical equation may sometimes indicate energy change (like Δ for heat), it does not provide information about observable changes such as colour change.
Q39. Which of the following is an element?
A. Water
B. Oxygen
C. Salt
D. Sugar
B. Oxygen
Oxygen is an element consisting of only one type of atom. Water, salt, and sugar are compounds.
Q40. What does a balanced equation indicate?
A. Same temperature
B. Same mass
C. Same volume
D. Same colour
B. Same mass
A balanced equation indicates that the total mass of reactants equals the total mass of products.
Q41. Which symbol is used for solid sodium chloride?
A. NaCl(g)
B. NaCl(l)
C. NaCl(s)
D. NaCl(aq)
C. NaCl(s)
The symbol (s) denotes the solid state. Sodium chloride is a solid at room temperature.
Q42. Chemical equations are written to save:
A. Energy
B. Money
C. Time and space
D. Heat
C. Time and space
Chemical equations provide a shorthand representation of reactions, saving time and space compared to writing them out in full sentences.
Q43. What is formed when magnesium burns in oxygen?
A. Magnesium chloride
B. Magnesium oxide
C. Magnesium sulphate
D. Magnesium nitrate
B. Magnesium oxide
Magnesium reacts with oxygen during combustion to form magnesium oxide (MgO).
Q44. In a chemical reaction, old bonds are:
A. Strengthened
B. Broken
C. Coloured
D. Frozen
B. Broken
Chemical reactions involve the breaking of bonds in reactants and the formation of new bonds to create products.
Q45. Which is always written first in a chemical equation?
A. Products
B. Reactants
C. Catalysts
D. Residues
B. Reactants
By convention, the reactants are always written on the left side of the arrow before the products.
Q46. What does the word “balanced” mean?
A. Equal atoms
B. Equal temperature
C. Equal volume
D. Equal colour
A. Equal atoms
A balanced chemical equation has an equal number of atoms of each element on both the reactant and product sides.
Q47. Which of the following is NOT a chemical reaction?
A. Burning paper
B. Rusting iron
C. Melting ice
D. Cooking food
C. Melting ice
Melting ice is a physical change where solid water changes to liquid water without forming a new substance.
Q48. A chemical equation shows:
A. Only reactants
B. Only products
C. Complete reaction
D. Only symbols
C. Complete reaction
A chemical equation typically shows the complete reaction, including all reactants and products involved.
Q49. What is formed when iron reacts with sulphur?
A. Mixture
B. Iron sulphide
C. Solution
D. Element
B. Iron sulphide
When iron and sulphur are heated together, they chemically combine to form the compound iron sulphide (FeS).
Q50. Why should chemical equations be balanced?
A. To look neat
B. To follow law of conservation of mass
C. To increase speed
D. To change products
B. To follow law of conservation of mass
Balancing chemical equations ensures they obey the law of conservation of mass, which states that matter cannot be created or destroyed.