Nokea
What is the general formula for an alkyl halide?
- A. Câ‚™Hâ‚‚â‚™
- B. CₙH₂ₙ₊₂
- C. Câ‚™H₂ₙ₊â‚X
- D. Câ‚™Hâ‚‚â‚™O
Correct Answer: C
Rationale: The correct answer is option C, 'Câ‚™H₂ₙ₊â‚X.' This is the general formula for an alkyl halide, where X represents a halogen atom (such as fluorine, chlorine, bromine, or iodine), and the hydrocarbon chain is represented by Câ‚™H₂ₙ₊â‚. Option A, 'Câ‚™Hâ‚‚â‚™,' is incorrect because it does not account for the presence of a halogen atom. Option B, 'Câ‚™H₂ₙ₊₂,' is incorrect as it represents an alkene, not an alkyl halide. Option D, 'Câ‚™Hâ‚‚â‚™O,' is also incorrect as it suggests the presence of oxygen, which is not characteristic of alkyl halides.
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A car skids on a wet road. What is the main force preventing the car from stopping?
- A. Friction
- B. Gravitational force
- C. Normal force from the road
- D. Air resistance
Correct Answer: A
Rationale: The correct answer is A: Friction. Friction is the force that opposes the motion of the car on the wet road surface, making it harder for the car to stop. When the car skids, the friction between the tires and the wet road surface is reduced, leading to a loss of traction and making it challenging for the car to come to a halt. Gravitational force (choice B) is the force that pulls objects toward each other due to gravity and does not directly impact the car's ability to stop on a wet road. The normal force from the road (choice C) is the force exerted by the road surface perpendicular to the car's tires and does not play a significant role in stopping the car. Air resistance (choice D) is the force that opposes the motion of an object through the air, but it is not the main force preventing the car from stopping on a wet road.
Bile, a digestive juice, is produced by which organ?
- A. Stomach
- B. Liver
- C. Pancreas
- D. Small intestine
Correct Answer: B
Rationale: Bile is a digestive juice produced by the liver. It is stored in the gallbladder and released into the small intestine to aid in the digestion and absorption of fats. The stomach (Choice A) produces gastric juices, not bile. The pancreas (Choice C) produces digestive enzymes and bicarbonate but not bile. The small intestine (Choice D) is where bile is released to aid in digestion but is not the organ that produces bile.
Which of the following substances is an example of an acidic gas?
- A. Nitrogen (Nâ‚‚)
- B. Carbon dioxide (COâ‚‚)
- C. Sulfur dioxide (SOâ‚‚)
- D. Oxygen (Oâ‚‚)
Correct Answer: C
Rationale: The correct answer is C, Sulfur dioxide (SOâ‚‚). Sulfur dioxide is an acidic gas because when dissolved in water, it forms sulfurous acid, which imparts acidic properties. Nitrogen (Nâ‚‚), carbon dioxide (COâ‚‚), and oxygen (Oâ‚‚) are not considered acidic gases. Nitrogen is a neutral gas, carbon dioxide forms a weakly acidic solution when dissolved in water, and oxygen is a neutral gas.
What happens to the frequency of a wave if its wavelength decreases while the speed remains constant?
- A. Frequency decreases
- B. Frequency increases
- C. Frequency remains constant
- D. Frequency becomes zero
Correct Answer: B
Rationale: The correct answer is B: Frequency increases. Frequency and wavelength are inversely proportional in a wave with a constant speed. When the wavelength decreases while the speed remains constant, the frequency must increase to maintain the constant speed of the wave. This relationship is governed by the equation: speed = frequency x wavelength. Choice A is incorrect as frequency increases when wavelength decreases. Choice C is incorrect as the frequency changes in this scenario. Choice D is incorrect as the frequency does not become zero but increases when the wavelength decreases.
T cells in the immune system can be categorized into different types. What type of T cell directly kills infected body cells?
- A. Helper T cells
- B. Cytotoxic T cells
- C. Regulatory T cells
- D. Memory T cells
Correct Answer: B
Rationale: Cytotoxic T cells directly kill infected body cells by recognizing specific antigens on the surface of infected cells and releasing cytotoxic substances to induce cell death, eliminating the infected cells. Helper T cells assist in coordinating the immune response, regulatory T cells help maintain immune tolerance, and memory T cells mount a faster and stronger response upon re-exposure to a previously encountered antigen. Therefore, the correct answer is cytotoxic T cells as they play a crucial role in directly targeting and destroying infected cells.