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1. How does increasing the concentration of reactants affect a chemical reaction?

• A. Decreases the reaction rate
• B. Increases the reaction rate
• C. Stops the reaction
• D. Has no effect

Correct answer: B

Rationale: Increasing the concentration of reactants leads to more reactant particles being available, which, in turn, increases the likelihood of successful collisions between particles. This higher frequency of collisions results in a higher reaction rate. Therefore, option B, 'Increases the reaction rate,' is the correct answer. Choice A, 'Decreases the reaction rate,' is incorrect because higher reactant concentration usually speeds up the reaction. Choice C, 'Stops the reaction,' is incorrect as increasing concentration promotes more collisions, enhancing the reaction. Choice D, 'Has no effect,' is incorrect because changing reactant concentration directly impacts the reaction rate in most cases.

2. Which gas is released during photosynthesis?

• A. Carbon dioxide
• B. Oxygen
• C. Nitrogen
• D. Helium

Correct answer: B

Rationale: During photosynthesis, plants utilize carbon dioxide and water to produce glucose and oxygen. Oxygen is released as a byproduct of this process, which is essential for the survival of most living organisms that depend on it for respiration. Therefore, the correct answer is oxygen. Choices A, C, and D are incorrect. Carbon dioxide is utilized in photosynthesis, nitrogen is not directly involved in the process, and helium is not a gas released during photosynthesis.

3. What is a balanced equation?

• A. A description where reactants and products are not equal
• B. An equation where the number of each type of atom is the same on both sides
• C. A chemical formula showing only reactants
• D. An equation without coefficients

Correct answer: B

Rationale: A balanced equation is one where the number of each type of atom is the same on both sides, fulfilling the law of conservation of mass. This principle ensures that the total number of atoms of each element is equal in both reactants and products, signifying that no atoms are created or destroyed, but rather rearranged. Choice A is incorrect because a balanced equation has equal numbers of atoms in the reactants and products. Choice C is incorrect as a balanced equation includes both reactants and products. Choice D is incorrect because coefficients are essential in balancing equations by adjusting the number of atoms present.

4. Which of the following can act as a catalyst in a chemical reaction?

• A. Enzyme
• B. Light
• C. Water
• D. Metal

Correct answer: A

Rationale: Enzymes are biological catalysts that speed up chemical reactions without being consumed. They lower the activation energy required for the reaction to occur, facilitating and accelerating the process. Choice B, Light, is not a catalyst but can sometimes trigger reactions by providing energy. Choice C, Water, and choice D, Metal, are not catalysts but can participate in reactions as reactants.

5. What does the mass of one mole of a substance represent?

• A. Atomic mass
• B. Mass number
• C. Molecular weight
• D. Molar mass

Correct answer: D

Rationale: The mass of one mole of a substance is represented by its molar mass. Molar mass is the mass of one mole of a substance and is expressed in grams per mole. It is calculated by summing the atomic masses of all atoms in a molecule. Therefore, the correct answer is D - 'Molar mass'. Choice A, 'Atomic mass', refers to the average mass of an atom of an element. Choice B, 'Mass number', is the total number of protons and neutrons in an atom's nucleus. Choice C, 'Molecular weight', is the average mass of a molecule relative to 1/12 of the mass of an atom of carbon-12.

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