📘 Study MCQs
Q1. What is a chemical equation?
A representation of a chemical reactionA chemical equation uses symbols and formulas to show what happens during a chemical reaction, including reactants, products, and their states.
Q2. The substances that take part in a chemical reaction are called:
ReactantsReactants are the starting materials that undergo chemical changes to form new substances.
Q3. The substances formed after a chemical reaction are called:
ProductsProducts are the new substances that are created as a result of a chemical reaction.
Q4. Which symbol separates reactants and products in a chemical equation?
→The arrow (→) separates the reactants (left side) from the products (right side) and indicates the direction of the reaction.
Q5. What does the plus sign (+) indicate in a chemical equation?
AndThe plus sign is used to separate multiple reactants or multiple products, meaning “and.”
Q6. Which of the following is a chemical change?
Rusting ironRusting forms a new substance (iron oxide), unlike melting, boiling, or cutting which are physical changes.
Q7. A chemical equation written in words is called:
Word equationA word equation uses the names of reactants and products instead of chemical formulas.
Q8. Which law is used to balance chemical equations?
Law of conservation of massThis law states that matter cannot be created or destroyed, so the number of each type of atom must be the same on both sides.
Q9. In a balanced chemical equation, the number of atoms on both sides is:
SameBalancing ensures the same quantity of each element appears on both reactant and product sides.
Q10. Which of the following is a word equation?
Hydrogen + Oxygen → WaterThis option uses words instead of chemical symbols to describe the reaction.
Q11. What does the symbol (s) indicate?
Solid(s) is the state symbol for a solid substance in a chemical equation.
Q12. The symbol (l) represents:
Liquid(l) indicates that the substance is in the liquid state.
Q13. Which symbol shows gaseous state?
(g)(g) stands for gas.
Q14. The symbol (aq) means:
Dissolved in water(aq) stands for aqueous, meaning the substance is dissolved in water.
Q15. A skeletal equation is:
Unbalanced equationA skeletal equation uses correct formulas but has not yet been balanced for atom counts.
Q16. Which of the following must be true for a balanced equation?
Same mass on both sidesThe law of conservation of mass requires total mass of reactants to equal total mass of products.
Q17. Which side of a chemical equation contains reactants?
Left sideReactants are always written on the left side of the arrow.
Q18. Products are written on which side of the equation?
Right sideProducts are always written on the right side of the arrow.
Q19. What does the arrow (→) mean?
GivesThe arrow means “yields,” “produces,” or “gives,” showing the direction of the reaction.
Q20. Which of the following shows a chemical reaction?
Burning coalBurning coal involves combustion, forming new substances like carbon dioxide and ash.
Q21. Which of the following is NOT shown by a chemical equation?
Speed of reactionA chemical equation indicates what reacts and what forms, but not how fast the reaction occurs.
Q22. Why are coefficients used in chemical equations?
To balance equationsCoefficients are numbers placed before formulas to equalize atom counts on both sides.
Q23. In H₂ + O₂ → H₂O, H₂ and O₂ are:
ReactantsH₂ and O₂ are written on the left side of the arrow, so they are the reactants.
Q24. In the reaction Mg + O₂ → MgO, MgO is a:
ProductMgO is written on the right side of the arrow, so it is the product.
Q25. What type of change is represented by a chemical equation?
Chemical changeA chemical equation represents a chemical reaction, which produces new substances.
Q26. Which of the following obeys the law of conservation of mass?
Balanced equationOnly a balanced equation has equal numbers of each atom on both sides, conserving mass.
Q27. What happens to atoms during a chemical reaction?
They are rearrangedAtoms are neither created nor destroyed; they are simply rearranged into new molecules.
Q28. Which symbol is used to show heat?
ΔThe Greek letter delta (Δ) written above the arrow indicates that heat is supplied to the reaction.
Q29. A chemical equation is balanced by changing:
CoefficientsOnly coefficients can be changed to balance an equation; subscripts and formulas must remain the same.
Q30. Which of the following is a balanced equation?
2H₂ + O₂ → 2H₂OThis equation has 4 H atoms and 2 O atoms on both sides.
Q31. Chemical equations are useful because they:
Show reactions clearlyEquations provide a concise, symbolic way to represent what happens in a chemical reaction.
Q32. Which of the following is a reactant?
Starting substanceReactants are the substances present at the beginning of a chemical reaction.
Q33. Which one is a chemical formula?
H₂OA chemical formula uses element symbols and subscripts to represent a compound.
Q34. What is the formula of carbon dioxide?
CO₂Carbon dioxide contains one carbon atom and two oxygen atoms.
Q35. Which change forms a new substance?
Rusting ironRusting produces iron oxide, a new chemical substance.
Q36. What is always conserved in a chemical reaction?
MassThe law of conservation of mass states that total mass remains constant in a chemical reaction.
Q37. Which part of the equation shows physical states?
State symbolsState symbols such as (s), (l), (g), and (aq) indicate the physical state of each substance.
Q38. A chemical equation does NOT show:
Colour changeWhile a colour change may occur, it is not indicated in a standard chemical equation.
Q39. Which of the following is an element?
OxygenOxygen (O₂) is an element; water, salt, and sugar are compounds.
Q40. What does a balanced equation indicate?
Same massA balanced equation shows that mass is conserved from reactants to products.
Q41. Which symbol is used for solid sodium chloride?
NaCl(s)(s) indicates the solid state, which is how sodium chloride normally appears.
Q42. Chemical equations are written to save:
Time and spaceEquations provide a shorthand way to describe reactions without writing long sentences.
Q43. What is formed when magnesium burns in oxygen?
Magnesium oxideMagnesium reacts with oxygen to form magnesium oxide (MgO).
Q44. In a chemical reaction, old bonds are:
BrokenChemical reactions involve breaking bonds in reactants and forming new bonds in products.
Q45. Which is always written first in a chemical equation?
ReactantsBy convention, reactants are written on the left side of the arrow.
Q46. What does the word “balanced” mean?
Equal atomsA balanced equation has the same number of each type of atom on both sides.
Q47. Which of the following is NOT a chemical reaction?
Melting iceMelting ice is a physical change (change of state) and does not produce new substances.
Q48. A chemical equation shows:
Complete reactionA chemical equation shows reactants, products, their states, and relative amounts.
Q49. What is formed when iron reacts with sulphur?
Iron sulphideIron and sulphur chemically combine to form the compound iron sulphide (FeS).
Q50. Why should chemical equations be balanced?
To follow law of conservation of massBalancing ensures that matter is neither created nor destroyed during the reaction.
