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Which of the following is a common property of bases?
- A. Conductivity in aqueous solutions
- B. Sour taste
- C. Reactivity with metals to produce hydrogen gas
- D. Turns red litmus paper blue
Correct Answer: D
Rationale: Bases are substances that can accept protons or donate hydroxide ions in a chemical reaction. One common property of bases is that they turn red litmus paper blue. This is a classic test to distinguish between acids (which turn blue litmus paper red) and bases. Conductivity in aqueous solutions (Option A) is a property of both acids and bases, but not unique to bases alone. Sour taste (Option B) is a property commonly associated with acids, not bases. Reactivity with metals to produce hydrogen gas (Option C) is a property of acids, particularly strong acids, but not bases.
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Fluorescent microscopy utilizes which property of certain molecules to create a visible image?
- A. Staining properties
- B. Light absorption
- C. Fluorescence emission
- D. Refraction
Correct Answer: C
Rationale: Fluorescent microscopy relies on the property of certain molecules to fluoresce when exposed to specific wavelengths of light. When these molecules absorb light energy, they become excited and then emit light at a longer wavelength, producing a visible image. This emitted light is what is used to create the image in fluorescent microscopy, making option C, fluorescence emission, the correct answer. Staining properties (option A) are used to enhance contrast in microscopy but are not the primary mechanism in fluorescent microscopy. Light absorption (option B) is involved in the excitation of fluorescent molecules but is not the property used to create the visible image. Refraction (option D) is the bending of light as it passes through different mediums and is not the property utilized in fluorescent microscopy.
The pH scale is used to indicate the concentration of:
- A. Hydrogen ions
- B. Oxygen
- C. Salts
- D. Sugar molecules
Correct Answer: A
Rationale: The pH scale is a measure of the concentration of hydrogen ions in a solution, representing its acidity or basicity. A lower pH value indicates higher hydrogen ion concentration and acidity, while a higher pH value indicates lower hydrogen ion concentration and basicity. Choice A, 'Hydrogen ions,' is the correct answer because the pH scale specifically measures the concentration of hydrogen ions in a solution. Choices B, C, and D are incorrect as the pH scale is not used to indicate the concentration of oxygen, salts, or sugar molecules.
What happens to the acceleration of an object when the force acting on it is increased, assuming the mass remains constant?
- A. Acceleration increases
- B. Acceleration decreases
- C. Acceleration remains constant
- D. Acceleration becomes zero
Correct Answer: A
Rationale: According to Newton's second law of motion, acceleration is directly proportional to the force acting on an object when the mass is constant. Therefore, if the force acting on an object is increased while the mass remains constant, the acceleration of the object will also increase. This relationship is described by the formula F = ma, where F is the force applied, m is the mass of the object, and a is the acceleration. When force increases, acceleration increases, and vice versa, as long as the mass stays the same. Choice B (Acceleration decreases) is incorrect because acceleration and force have a direct relationship. Choice C (Acceleration remains constant) is incorrect because acceleration changes in response to changes in force. Choice D (Acceleration becomes zero) is incorrect because increasing force does not make acceleration zero; it actually increases it.
Which type of lens focuses parallel light rays to a single point?
- A. Concave lens
- B. Convex lens
- C. Cylindrical lens
- D. Plano lens
Correct Answer: B
Rationale: A convex lens focuses parallel light rays to a single point by causing them to converge. This lens is thicker in the center than at the edges, which helps in converging the light rays. Convex lenses are commonly used for tasks like magnification and focusing due to their ability to bring distant light rays to a single focal point. Choice A, the concave lens, diverges light rays rather than converging them, making it incorrect. Choice C, the cylindrical lens, is designed to focus light along one axis rather than converging parallel light rays to a single point. Choice D, the plano lens, has no curvatures to bend or focus light rays, so it does not converge parallel light rays.
What happens to the gravitational potential energy of an object as it falls freely?
- A. It decreases
- B. It increases
- C. It remains constant
- D. It becomes zero
Correct Answer: A
Rationale: The correct answer is A: 'It decreases.' When an object falls freely, its height decreases, resulting in a decrease in gravitational potential energy. The potential energy is converted into kinetic energy as the object accelerates due to gravity. This conversion process continues until the object reaches the ground or its lowest point, where the gravitational potential energy is minimal or zero. Choice B is incorrect because gravitational potential energy decreases, not increases, during free fall. Choice C is incorrect as gravitational potential energy changes due to the change in height. Choice D is incorrect as the gravitational potential energy does not instantly become zero but decreases gradually as the object falls.