Question 1:

The correct answer is A. is chemically unchanged at the end of the reaction.

Explanation:
By definition, a catalyst is a substance that speeds up the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy. Importantly, the catalyst is not consumed by the reaction—it may participate temporarily in intermediate steps, but it is chemically unchanged at the end of the reaction and can be used again.

Here is why the other options are incorrect:

• B. Is chemically changed at the end of the reaction – Incorrect. If it were chemically changed, it would be a reactant, not a catalyst. A catalyst is regenerated in its original form.

• C. Does not take part in the reaction – Incorrect. A catalyst does take part in the reaction temporarily (forming intermediate species), but it is restored at the end. It does not simply "watch" from the sidelines.

• D. Changes the products made – Incorrect. A catalyst does not alter the products of a reaction; it only affects the rate at which the products are formed. The final products and the overall reaction equation remain the same.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 2:

The correct answer is C. providing an alternative pathway with lower activation energy.

Explanation:
Catalysts work by offering a different reaction route (mechanism) that has a lower activation energy than the uncatalyzed reaction. This means that more particles will have enough energy to successfully react at a given temperature, which increases the rate of reaction without the catalyst being consumed.

Here is why the other options are incorrect:

• A. Giving more particles sufficient energy to react – Incorrect. A catalyst does not add energy to the particles; it lowers the energy barrier (activation energy) that they need to overcome. (Increasing temperature is what gives particles more kinetic energy.)

• B. Increasing the frequency of collisions between reactants – Incorrect. While this would increase reaction rate, it is not how catalysts work. (Increasing concentration or pressure increases collision frequency.) A catalyst changes the effectiveness of collisions by lowering the energy requirement, not the number of collisions.

• D. Providing an alternative pathway with higher activation energy – Incorrect. A higher activation energy would actually slow down the reaction, which is the opposite of what a catalyst does.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 3:

The activation energy is the energy required to reach the peak of the energy barrier from the reactants' level. The higher peak represents the uncatalysed path.

Answer: A

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 4:

A catalyst provides an alternative pathway with a lower activation energy, represented by the lower peak (shown by the green thin line).

Answer: B

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 5:

The correct answer is D. the minimum energy required by reactant particles for a reaction to occur.

Explanation:
Activation energy is defined as the minimum amount of energy that colliding reactant particles must possess in order for a successful collision to occur—one that results in a chemical reaction. If the particles do not have at least this much energy, they will simply bounce off each other without reacting, even if they collide in the correct orientation.

Here is why the other options are incorrect:

• A. The energy supplied to the reactants during a reaction – Incorrect. This describes the energy input (e.g., heating), not the specific energy barrier that must be overcome for the reaction to proceed.

• B. The difference in energy between reactants and products – Incorrect. This describes the overall 'enthalpy change (ΔH)' of a reaction, which indicates whether a reaction is exothermic or endothermic, not the activation energy.

• C. The minimum energy required by product particles for a reaction to occur – Incorrect. Activation energy applies to the reactant particles, not the products. It is the energy needed to reach the transition state from the reactants' side.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 6:

The correct answer is D. X and Z.

Explanation:
A catalyst is a substance that:

1. Speeds up the rate of a reaction (increases the volume of oxygen collected compared to the "none" control).

2. Is chemically unchanged at the end of the reaction (its mass remains the same before and after).

Let's analyze each metal oxide:

• X – Volume of O₂ = 82 cm³ (greater than 0, so it speeds up the reaction). Mass = 1 g before and 1 g after (chemically unchanged). → Catalyst

• Y – Volume of O₂ = 158 cm³ (greater than 0, so it speeds up the reaction). Mass = 1 g before but 0.6 g after (mass changed). → Not a catalyst (it was consumed or reacted)

• Z – Volume of O₂ = 34 cm³ (greater than 0, so it speeds up the reaction). Mass = 1 g before and 1 g after (chemically unchanged). → Catalyst

• W – Volume of O₂ = 0 cm³ (same as the control, so it does not speed up the reaction). → Not a catalyst

Therefore, only X and Z meet both criteria for being catalysts.

Here is why the other options are incorrect:

• A. All of them – Incorrect because Y changed mass and W did not speed up the reaction.

• B. X, Y and Z – Incorrect because Y changed mass.

• C. X and Y – Incorrect because Y changed mass and is not a catalyst.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 7:

Correct answer: A. metal oxide X.

Explanation:
For a substance to be a catalyst, it must speed up the reaction and remain chemically unchanged (its mass must stay the same before and after the reaction).

• X – Speeds up the reaction (82 cm³ of oxygen) and mass remains 1 g → true catalyst.

• Y – Speeds up the reaction the most (158 cm³), but its mass changes from 1 g to 0.6 g → not a catalyst (it is consumed).

• Z – Speeds up the reaction (34 cm³) and mass remains 1 g → true catalyst, but less effective than X.

• W – Produces 0 cm³ of oxygen → no catalytic effect.

Since Y is not a true catalyst, it cannot be considered the "most effective catalyst." Among the actual catalysts (X and Z), X produces the higher volume of oxygen (82 cm³ vs 34 cm³), so it is the most effective true catalyst.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 8:

The correct answer is C. in a measuring cylinder by the downward displacement of water.

Explanation:
Hydrogen gas is less dense than air and is also insoluble in water. The most accurate and practical way to collect and measure the volume of hydrogen gas in a school laboratory is by using the downward displacement of water (also known as water displacement). In this method, a gas syringe or an inverted measuring cylinder filled with water is placed over the reaction vessel. As hydrogen gas is produced, it bubbles up and displaces the water downward, allowing the volume of gas to be read directly from the cylinder.

Here is why the other options are incorrect:

• A. In a measuring cylinder by the downward displacement of air – Incorrect. Hydrogen is less dense than air, so it would rise and escape if you tried to collect it by downward displacement of air. (Downward displacement of air is used for gases that are denser than air, like carbon dioxide.)

• B. In a measuring cylinder by the upward displacement of air – Incorrect. While hydrogen could be collected this way (since it rises), it is difficult to get pure hydrogen and accurate volume measurements because air mixes with it easily.

• D. Using an electronic balance – Incorrect. An electronic balance measures mass, not volume. While you could indirectly track the reaction by measuring the loss of mass as hydrogen escapes, this would not directly give you the volume of hydrogen collected at regular time intervals, which is what the student needs to measure the rate of reaction.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 9:

The correct answer is C. use the same mass of zinc and volume of sulfuric acid each time.

Explanation:
For a fair test (controlled experiment), only the independent variable (the mass of copper(II) sulfate) should change. All other factors that could affect the rate of reaction must be kept constant (controlled).

The mass of zinc and the volume (and concentration) of sulfuric acid are key factors that affect the rate of hydrogen production. If these were changed between experiments, you could not be sure that any difference in reaction rate was due to the catalyst mass alone—it might be due to having more zinc or more acid.

Here is why the other options are incorrect:

• A. Repeat the experiment 3 times for each mass of copper(II) sulfate – This is good practice for reliability (to check for consistent results), but it does not ensure a fair test. A fair test is about controlling variables, not repetition.

• B. Use a range of at least 5 different masses of copper(II) sulfate – This is good for producing a valid conclusion and identifying trends, but again, it does not ensure a fair test. It relates to the range of data, not controlling other variables.

• D. Repeat the experiment at different temperatures – This would actually introduce a new independent variable (temperature), making the test unfair. Temperature must be kept constant if you are investigating the effect of catalyst mass.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.

Question 10:

The correct answer is B. an enzyme.

Explanation:
Enzymes are biological catalysts, typically proteins, that speed up the rate of chemical reactions in living organisms. They work by lowering the activation energy of a reaction, just like other catalysts, and remain chemically unchanged at the end of the reaction.

Here is why the other options are incorrect:

• A. An inhibitor – Incorrect. An inhibitor is a substance that slows down or stops a reaction, often by blocking the active site of an enzyme. It is the opposite of a catalyst.

• C. An isotope – Incorrect. An isotope is a variant of an element that has the same number of protons but a different number of neutrons (e.g., carbon-12 vs. carbon-14). This has nothing to do with catalysis.

• D. A substrate – Incorrect. A substrate is the reactant molecule that an enzyme acts upon (e.g., the molecule that fits into the enzyme's active site). It is not the catalyst itself.

*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret.
Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.