📌 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.
📘 Study MCQs
Q1. What helps us determine that a chemical reaction has taken place?
• Only a change in state
• Only a change in colour
• Change in state, colour, temperature, or evolution of gas
• Only evolution of gas
Answer: Change in state, colour, temperature, or evolution of gas
According to the text, observations like a change in state, colour, temperature, or the evolution of a gas help determine if a chemical reaction has occurred.
Q2. What is the chemical change described when a magnesium ribbon is burnt in oxygen?
• Magnesium oxide is converted to magnesium.
• Magnesium gets converted to magnesium oxide.
• Oxygen gets converted to magnesium.
• No new substance is formed.
Answer: Magnesium gets converted to magnesium oxide.
The text states: “when a magnesium ribbon is burnt in oxygen, it gets converted to magnesium oxide.”
Q3. What is the simplest way to write a description of a chemical reaction?
• As a paragraph
• As a word-equation
• As a detailed essay
• As a single symbol
Answer: As a word-equation
The text says the simplest shorter way to write a chemical reaction is in the form of a word-equation.
Q4. In the word-equation: Magnesium + Oxygen → Magnesium oxide, what are ‘Magnesium’ and ‘Oxygen’ called?
• Products
• Reactants
• Results
• Mixtures
Answer: Reactants
The substances that undergo chemical change (magnesium and oxygen) are called reactants.
Q5. In a word-equation, what does the arrow (→) show?
• The direction of the reaction
• That reactants and products are equal
• A plus sign
• The temperature of the reaction
Answer: The direction of the reaction
The arrow head points towards the products and shows the direction of the reaction.
Q6. In a word-equation, where are the reactants written?
• On the Right Hand Side (RHS) with a plus sign
• On the Left Hand Side (LHS) with a plus sign
• Above the arrow
• Below the arrow
Answer: On the Left Hand Side (LHS) with a plus sign
Reactants are written on the left-hand side (LHS) with a plus sign (+) between them.
Q7. In a word-equation, where are the products written?
• On the Left Hand Side (LHS)
• On the Right Hand Side (RHS) with a plus sign
• On both sides
• Nowhere
Answer: On the Right Hand Side (RHS) with a plus sign
Products are written on the right-hand side (RHS) with a plus sign (+) between them.
Q8. What is a more concise way to represent a chemical equation than a word-equation?
• Using longer descriptions
• Using chemical formulae instead of words
• Using pictures only
• Using only numbers
Answer: Using chemical formulae instead of words
Chemical equations can be made more concise and useful if we use chemical formulae instead of words.
Q9. What is a skeletal chemical equation?
• An equation with the same number of atoms on both sides
• An unbalanced equation where mass is not conserved
• An equation written only in words
• An equation with state symbols
Answer: An unbalanced equation where mass is not conserved
A skeletal chemical equation is unbalanced because the mass (and number of atoms of each element) is not the same on both sides.
Q10. Which law states that mass can neither be created nor destroyed in a chemical reaction?
• Law of constant proportions
• Law of conservation of mass
• Law of multiple proportions
• Newton’s law
Answer: Law of conservation of mass
The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.
Q11. According to the law of conservation of mass, what remains the same before and after a chemical reaction?
• The number of molecules of each compound
• The physical state of each element
• The number of atoms of each element
• The colour of the substances
Answer: The number of atoms of each element
The number of atoms of each element remains the same, before and after a chemical reaction.
Q12. Why do we need to balance a chemical equation?
• To make it look longer
• To obey the law of conservation of mass
• To change the reactants
• To include the temperature
Answer: To obey the law of conservation of mass
We balance an equation so that the number of atoms of each element is equal on both sides, obeying the law of conservation of mass.
Q13. In the balanced equation Zn + H₂SO₄ → ZnSO₄ + H₂, how many hydrogen atoms are on each side?
• 1
• 2
• 3
• 4
Answer: 2
As per the atom count table in the text, the number of hydrogen (H) atoms is 2 on both the reactant and product sides.
Q14. What is the first step suggested for balancing a chemical equation?
• Change the formulae of the compounds.
• Draw boxes around each formula.
• Start balancing the oxygen atoms first.
• Write the physical states.
Answer: Draw boxes around each formula.
Step I is to draw boxes around each formula and not change anything inside the boxes while balancing.
Q15. When starting to balance an equation, it is often convenient to start with the compound that has what?
• The minimum number of atoms
• The colour change
• The maximum number of atoms
• The gaseous state
Answer: The maximum number of atoms
It is often convenient to start balancing with the compound that contains the maximum number of atoms.
Q16. What does the symbol (s) represent in a chemical equation?
• Solution
• Solid state
• Liquid state
• Gas state
Answer: Solid state
The solid state of reactants and products is represented by the notation (s).
Q17. What does the symbol (l) represent in a chemical equation?
• Light
• Liquid state
• Large quantity
• Less than
Answer: Liquid state
The liquid state of reactants and products is represented by the notation (l).
Q18. What does the symbol (g) represent in a chemical equation?
• Gravitational force
• Green colour
• Gas state
• Grams
Answer: Gas state
The gaseous state of reactants and products is represented by the notation (g).
Q19. What does the symbol (aq) represent in a chemical equation?
• A quantity
• Aquatic
• Aqueous (solution in water)
• Air quality
Answer: Aqueous (solution in water)
The word aqueous (aq) is written if the reactant or product is present as a solution in water.
Q20. In the equation 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g), what does (g) with H₂O indicate?
• Water is ice.
• Water is a liquid.
• Water is in the form of steam.
• Water is dissolved.
Answer: Water is in the form of steam.
The symbol (g) is used with H₂O to indicate that in this reaction water is used in the form of steam.
Q21. Are physical states always included in a chemical equation?
• Yes, always.
• No, they are always excluded.
• Usually they are not included unless necessary to specify them.
• Only for solids.
Answer: Usually they are not included unless necessary to specify them.
The text states: “Usually physical states are not included in a chemical equation unless it is necessary to specify them.”
Q22. Where are reaction conditions like temperature or catalyst indicated in a chemical equation?
• Before the reactants
• After the products
• Above and/or below the arrow in the equation
• Only in the word-equation
Answer: Above and/or below the arrow in the equation
Sometimes the reaction conditions are indicated above and/or below the arrow in the equation.
Q23. In the reaction for the formation of methanol, what condition is written below the arrow?
• Sunlight
• 340 atm
• Chlorophyll
• (s)
Answer: 340 atm
For the reaction CO(g) + 2H₂(g) → CH₃OH(l), the condition ‘340 atm’ is indicated below the arrow.
Q24. In the photosynthesis equation, what are the conditions mentioned above the arrow?
• 340 atm
• Sunlight / Chlorophyll
• High temperature
• (aq)
Answer: Sunlight / Chlorophyll
For the photosynthesis reaction, the conditions ‘sunlight / chlorophyll’ are indicated above the arrow.
Q25. What is the product when hydrogen reacts with chlorine according to the word-equation?
• Hydrogen chloride
• Hydrogen peroxide
• Chlorine water
• Hydrogen gas
Answer: Hydrogen chloride
The word-equation given is: Hydrogen + Chlorine → Hydrogen chloride.
Q26. In a chemical reaction, do atoms of one element change into atoms of another element?
• Yes, always.
• No, they never do.
• Sometimes they do.
• Only in decomposition reactions.
Answer: No, they never do.
The text states that during a chemical reaction, atoms of an element do not change into those of another element.
Q27. What do chemical reactions actually involve at the atomic level?
• Disappearance of atoms
• Creation of new atoms
• Breaking and making of bonds between atoms
• Only mixing of atoms
Answer: Breaking and making of bonds between atoms
Chemical reactions involve the breaking and making of bonds between atoms to produce new substances.
Q28. What is the new substance formed in the reaction of zinc and sulphuric acid?
• Zinc and hydrogen
• Zinc sulphate and hydrogen
• Sulphuric acid only
• Zinc oxide
Answer: Zinc sulphate and hydrogen
The word-equation is: Zinc + Sulphuric acid → Zinc sulphate + Hydrogen.
Q29. If the number of atoms of each element is the same on both sides of an equation, what is it called?
• A skeletal equation
• A word-equation
• An unbalanced equation
• A balanced chemical equation
Answer: A balanced chemical equation
When the number of atoms of each element is the same on both sides, the equation is balanced.
Q30. What should you NOT change while balancing a chemical equation?
• The coefficients in front of formulae
• Anything inside the boxes drawn around formulae
• The order of reactants
• The physical states
Answer: Anything inside the boxes drawn around formulae
Step I instructs to draw boxes around each formula and not change anything inside the boxes while balancing.
Q31. What does the ‘+’ sign between reactants in a word-equation represent?
• They are multiplied.
• They are added together.
• They are in different states.
• They are products.
Answer: They are added together.
The reactants are written on the LHS with a plus sign (+) between them, indicating they combine.
Q32. From the atom count for Fe + H₂O → Fe₃O₄ + H₂, how many iron atoms are on the product side?
• 1
• 3
• 4
• 2
Answer: 3
The table in the text shows the number of iron (Fe) atoms in the products (RHS) as 3 (from Fe₃O₄).
Q33. From the atom count for Fe + H₂O → Fe₃O₄ + H₂, how many oxygen atoms are on the reactant side?
• 1
• 4
• 2
• 3
Answer: 1
The table in the text shows the number of oxygen (O) atoms in the reactants (LHS) as 1 (from H₂O).
Q34. What information does a balanced chemical equation *without* state symbols NOT give?
• The identities of reactants and products
• The physical states of reactants and products
• The ratio of molecules/atoms
• The direction of the reaction
Answer: The physical states of reactants and products
A balanced equation without state symbols does not provide information about the physical state (solid, liquid, etc.) of each substance.
Q35. To make a chemical equation more informative, what can be added along with the chemical formulae?
• The price of chemicals
• The physical states of reactants and products
• The name of the scientist
• The date of the reaction
Answer: The physical states of reactants and products
The physical states are mentioned along with chemical formulae to make the equation more informative.
Q36. In the final balanced form of the iron and steam reaction, what is the coefficient of H₂?
• 2
• 3
• 4
• 1
Answer: 4
The final balanced equation given is 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g). The coefficient of H₂ is 4.
Q37. What does a chemical equation represent?
• Only the speed of a reaction
• The identities and proportions of reactants and products
• Only the colour changes
• Only the gases involved
Answer: The identities and proportions of reactants and products
A chemical equation symbolically represents the identities and relative amounts of reactants and products in a chemical change.
Q38. What is the first step in going from a word description to a chemical equation?
• Balance the atoms.
• Write the word-equation.
• Add state symbols.
• Write the skeletal formula equation.
Answer: Write the word-equation.
The initial step shown in the text is to write the description as a simpler word-equation.
Q39. What must be true for a chemical equation to obey the law of conservation of mass?
• It must be a word-equation.
• It must be balanced.
• It must have state symbols.
• It must have an arrow.
Answer: It must be balanced.
Only a balanced chemical equation ensures the number of atoms (and hence mass) is conserved.
Q40. In the photosynthesis equation 6CO₂(aq) + 6H₂O → C₆H₁₂O₆(aq) + 6O₂(g), what is the physical state of glucose?
• (s)
• (g)
• (l)
• (aq)
Answer: (aq)
In the equation, glucose (C₆H₁₂O₆) is written with (aq), meaning it is in aqueous solution.
Q41. What is the primary purpose of the arrow in a chemical equation?
• To separate reactants from products
• To show the reaction yields products from reactants
• To indicate heat is applied
• To show the reaction is reversible
Answer: To show the reaction yields products from reactants
The arrow points from reactants to products, showing the direction of the transformation.
Q42. According to the text, what does NOT happen to atoms during a chemical reaction?
• They form new bonds.
• They do not disappear from the mixture.
• They do not appear from elsewhere.
• They change into atoms of another element.
Answer: They change into atoms of another element.
Atoms of an element do not change into those of another element during a chemical reaction.
Q43. What is the reactant in the burning of magnesium?
• Magnesium oxide only
• Oxygen only
• Magnesium and Oxygen
• Heat
Answer: Magnesium and Oxygen
In the reaction, magnesium and oxygen are the substances that undergo chemical change, so they are the reactants.
Q44. In the skeleton equation Mg + O₂ → MgO, why is it unbalanced?
• The formula of MgO is wrong.
• The number of oxygen atoms is not equal on both sides.
• The plus sign is missing.
• The arrow is missing.
Answer: The number of oxygen atoms is not equal on both sides.
On the left, there are 2 O atoms (O₂). On the right, there is only 1 O atom (in MgO). The atoms are not equal.
Q45. Which step in balancing involves listing the number of atoms of each element?
• Step I
• Step II
• Step III
• Step VII
Answer: Step II
Step II is: “List the number of atoms of different elements present in the unbalanced equation.”
Q46. What is the main characteristic of a skeletal chemical equation?
• It is balanced.
• It has state symbols.
• It is unbalanced.
• It has reaction conditions.
Answer: It is unbalanced.
A skeletal chemical equation is an unbalanced equation.
Q47. What is the correct word-equation for the reaction of sodium and water?
• Sodium + Water → Sodium oxide + Hydrogen
• Sodium + Water → Sodium hydroxide + Hydrogen
• Sodium hydroxide → Sodium + Water
• Sodium + Hydrogen → Sodium hydroxide
Answer: Sodium + Water → Sodium hydroxide + Hydrogen
The text lists this as one of the examples: Sodium + Water → Sodium hydroxide + Hydrogen.
Q48. What are the products in the reaction: Barium chloride + Aluminium sulphate → ?
• Barium sulphate + Aluminium chloride
• Barium aluminium + Chloride sulphate
• Barium chloride + Aluminium sulphate
• Barium oxide + Aluminium oxide
Answer: Barium sulphate + Aluminium chloride
The text lists this as one of the examples: Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride.
Q49. In the final balanced equation, what is the physical state of the product iron oxide (Fe₃O₄)?
• (g)
• (aq)
• (l)
• (s)
Answer: (s)
In the final equation 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g), Fe₃O₄ is marked as (s) for solid.
Q50. Based on the text, what is the ultimate goal of writing and balancing a chemical equation?
• To make it look complex
• To represent a chemical change accurately and informatively
• To use as many symbols as possible
• To hide the reaction details
Answer: To represent a chemical change accurately and informatively
The process leads to a balanced equation, often with added state symbols or conditions, which accurately and informatively represents the chemical change.