π How to Use
First read the questions carefully using the Read section. Use the Details button to understand concepts clearly. After completing reading, click Practice Quiz to test yourself.
π Study MCQs
Q1. What is a chemical equation?
β’ A statement of physical change
β’ A representation of a chemical reaction
β’ A mathematical formula
β’ A physical law
Answer: A representation of a chemical reaction
A chemical equation shows a chemical reaction using words or symbols.
Q2. The substances that take part in a chemical reaction are called:
β’ Products
β’ Reactants
β’ Elements
β’ Compounds
Answer: Reactants
Reactants are the substances present at the start of a reaction.
Q3. The substances formed after a chemical reaction are called:
β’ Reactants
β’ Residues
β’ Products
β’ Mixtures
Answer: Products
Products are the new substances formed after a chemical reaction.
Q4. Which symbol separates reactants and products in a chemical equation?
β’ +
β’ β
β’ Γ
Answer: β
The arrow shows the direction of the reaction from reactants to products.
Q5. What does the plus sign (+) indicate in a chemical equation?
β’ Gives
β’ Equals
β’ And
β’ Heat
Answer: And
The plus sign means that two or more substances react together.
Q6. Which of the following is a chemical change?
β’ Melting ice
β’ Boiling water
β’ Rusting iron
β’ Cutting paper
Answer: Rusting iron
Rusting forms a new substance, iron oxide, so it is a chemical change.
Q7. A chemical equation written in words is called:
β’ Balanced equation
β’ Word equation
β’ Skeletal equation
β’ Symbolic equation
Answer: Word equation
A word equation uses names of substances instead of symbols.
Q8. Which law is used to balance chemical equations?
β’ Law of gravity
β’ Law of conservation of mass
β’ Law of motion
β’ Law of energy
Answer: Law of conservation of mass
Mass is neither created nor destroyed in a chemical reaction.
Q9. In a balanced chemical equation, the number of atoms on both sides is:
β’ Different
β’ Unequal
β’ Same
β’ Random
Answer: Same
The number of atoms of each element remains the same on both sides.
Q10. Which of the following is a word equation?
β’ Hβ + Oβ β HβO
β’ Hydrogen + Oxygen β Water
β’ 2Hβ + Oβ β 2HβO
β’ HβO β Hβ + Oβ
Answer: Hydrogen + Oxygen β Water
A word equation uses words instead of chemical symbols.
Q11. What does the symbol (s) indicate?
β’ Solid
β’ Solution
β’ Gas
β’ Liquid
Answer: Solid
The symbol (s) shows that the substance is in solid state.
Q12. The symbol (l) represents:
β’ Liquid
β’ Light
β’ Layer
β’ Lime
Answer: Liquid
(l) indicates that the substance is in liquid state.
Q13. Which symbol shows gaseous state?
β’ (s)
β’ (l)
β’ (aq)
β’ (g)
Answer: (g)
(g) is used to represent gases in chemical equations.
Q14. The symbol (aq) means:
β’ Solid
β’ Liquid
β’ Gas
β’ Dissolved in water
Answer: Dissolved in water
(aq) shows that the substance is dissolved in water.
Q15. A skeletal equation is:
β’ Balanced equation
β’ Unbalanced equation
β’ Word equation
β’ Nuclear equation
Answer: Unbalanced equation
A skeletal equation shows formulas but is not balanced.
Q16. Which of the following must be true for a balanced equation?
β’ Same number of molecules
β’ Same mass on both sides
β’ Same volume
β’ Same colour
Answer: Same mass on both sides
Balanced equations obey the law of conservation of mass.
Q17. Which side of a chemical equation contains reactants?
β’ Right side
β’ Left side
β’ Below arrow
β’ Above arrow
Answer: Left side
Reactants are always written on the left side.
Q18. Products are written on which side of the equation?
β’ Left side
β’ Below arrow
β’ Right side
β’ Above arrow
Answer: Right side
Products appear on the right side of a chemical equation.
Q19. What does the arrow (β) mean?
β’ Equals
β’ Plus
β’ Gives
β’ Heat
Answer: Gives
The arrow shows what the reactants change into.
Q20. Which of the following shows a chemical reaction?
β’ Breaking glass
β’ Melting wax
β’ Burning coal
β’ Freezing water
Answer: Burning coal
Burning coal produces new substances, so it is a chemical reaction.
Q21. Which of the following is NOT shown by a chemical equation?
β’ Reactants
β’ Products
β’ Mass balance
β’ Speed of reaction
Answer: Speed of reaction
Chemical equations do not show how fast a reaction occurs.
Q22. Why are coefficients used in chemical equations?
β’ To change formulas
β’ To balance equations
β’ To add substances
β’ To remove atoms
Answer: To balance equations
Coefficients help make the number of atoms equal on both sides.
Q23. In Hβ + Oβ β HβO, Hβ and Oβ are:
β’ Products
β’ Reactants
β’ Catalysts
β’ Residues
Answer: Reactants
Hβ and Oβ take part in the reaction, so they are reactants.
Q24. In the reaction Mg + Oβ β MgO, MgO is a:
β’ Reactant
β’ Element
β’ Product
β’ Mixture
Answer: Product
MgO is formed as a result of the reaction.
Q25. What type of change is represented by a chemical equation?
β’ Physical change
β’ Chemical change
β’ Temporary change
β’ Reversible change
Answer: Chemical change
Chemical equations represent chemical changes only.
Q26. Which of the following obeys the law of conservation of mass?
β’ Word equation
β’ Skeletal equation
β’ Balanced equation
β’ Unbalanced equation
Answer: Balanced equation
Only balanced equations follow the law of conservation of mass.
Q27. What happens to atoms during a chemical reaction?
β’ They are destroyed
β’ They are created
β’ They are rearranged
β’ They disappear
Answer: They are rearranged
Atoms are rearranged to form new substances.
Q28. Which symbol is used to show heat?
β’ +
β’ Ξ
β’ β
Answer: Ξ
The symbol Ξ indicates heating.
Q29. A chemical equation is balanced by changing:
β’ Chemical formulas
β’ Number of atoms
β’ Coefficients
β’ Symbols
Answer: Coefficients
Only coefficients are changed to balance equations.
Q30. Which of the following is a balanced equation?
β’ Hβ + Oβ β HβO
β’ 2Hβ + Oβ β 2HβO
β’ Hβ + O β HβO
β’ H + Oβ β HβO
Answer: 2Hβ + Oβ β 2HβO
The number of atoms is equal on both sides.
Q31. Chemical equations are useful because they:
β’ Show reactions clearly
β’ Increase weight
β’ Change colour
β’ Slow reactions
Answer: Show reactions clearly
They help us understand chemical reactions easily.
Q32. Which of the following is a reactant?
β’ Substance formed
β’ Starting substance
β’ Final product
β’ Residue
Answer: Starting substance
Reactants are present at the beginning of a reaction.
Q33. Which one is a chemical formula?
β’ Water
β’ Liquid
β’ HβO
β’ Solid
Answer: HβO
HβO is the chemical formula of water.
Q34. What is the formula of carbon dioxide?
β’ CO
β’ COβ
β’ CβO
β’ COβ
Answer: COβ
Carbon dioxide contains one carbon and two oxygen atoms.
Q35. Which change forms a new substance?
β’ Boiling water
β’ Melting ice
β’ Rusting iron
β’ Freezing milk
Answer: Rusting iron
Rusting forms iron oxide, a new substance.
Q36. What is always conserved in a chemical reaction?
β’ Volume
β’ Mass
β’ Colour
β’ Shape
Answer: Mass
Mass remains constant during a chemical reaction.
Q37. Which part of the equation shows physical states?
β’ Coefficients
β’ Symbols
β’ State symbols
β’ Arrow
Answer: State symbols
State symbols show whether substances are solid, liquid, gas, or aqueous.
Q38. A chemical equation does NOT show:
β’ Reactants
β’ Products
β’ Energy change
β’ Colour change
Answer: Colour change
Colour change is not shown in a chemical equation.
Q39. Which of the following is an element?
β’ Water
β’ Oxygen
β’ Salt
β’ Sugar
Answer: Oxygen
Oxygen is a pure element.
Q40. What does a balanced equation indicate?
β’ Same temperature
β’ Same mass
β’ Same volume
β’ Same colour
Answer: Same mass
Balanced equations follow conservation of mass.
Q41. Which symbol is used for solid sodium chloride?
β’ NaCl(g)
β’ NaCl(l)
β’ NaCl(s)
β’ NaCl(aq)
Answer: NaCl(s)
(s) shows solid state.
Q42. Chemical equations are written to save:
β’ Energy
β’ Money
β’ Time and space
β’ Heat
Answer: Time and space
Symbols make equations short and easy to write.
Q43. What is formed when magnesium burns in oxygen?
β’ Magnesium chloride
β’ Magnesium oxide
β’ Magnesium sulphate
β’ Magnesium nitrate
Answer: Magnesium oxide
Magnesium reacts with oxygen to form magnesium oxide.
Q44. In a chemical reaction, old bonds are:
β’ Strengthened
β’ Broken
β’ Coloured
β’ Frozen
Answer: Broken
Old bonds break and new bonds are formed.
Q45. Which is always written first in a chemical equation?
β’ Products
β’ Reactants
β’ Catalysts
β’ Residues
Answer: Reactants
Reactants are written on the left side first.
Q46. What does the word βbalancedβ mean?
β’ Equal atoms
β’ Equal temperature
β’ Equal volume
β’ Equal colour
Answer: Equal atoms
Balanced means equal number of atoms on both sides.
Q47. Which of the following is NOT a chemical reaction?
β’ Burning paper
β’ Rusting iron
β’ Melting ice
β’ Cooking food
Answer: Melting ice
Melting ice is a physical change.
Q48. A chemical equation shows:
β’ Only reactants
β’ Only products
β’ Complete reaction
β’ Only symbols
Answer: Complete reaction
It shows both reactants and products of a reaction.
Q49. What is formed when iron reacts with sulphur?
β’ Mixture
β’ Iron sulphide
β’ Solution
β’ Element
Answer: Iron sulphide
Iron and sulphur combine to form iron sulphide.
Q50. Why should chemical equations be balanced?
β’ To look neat
β’ To follow law of conservation of mass
β’ To increase speed
β’ To change products
Answer: To follow law of conservation of mass
Balancing ensures mass is neither created nor destroyed.