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Which of the following describes the covalent bonds linking two carbon atoms in an acetylene molecule (C2H2)?
- A. Single bond
- B. Triple bond
- C. Double bond
- D. Quadruple bond
Correct Answer: B
Rationale: The correct answer is B, 'Triple bond.' In an acetylene molecule (C2H2), the covalent bonds linking the two carbon atoms form a triple bond. A triple bond involves the sharing of three pairs of electrons between the carbon atoms, resulting in a very strong bond. Acetylene is a reactive compound used in various chemical processes due to its high reactivity, facilitated by the strength of the triple bond. This bond imparts stability to the molecular structure of acetylene, contributing to its unique properties and applications in organic chemistry.
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Which substance protects the body from ultraviolet rays?
- A. Keratin
- B. Sebum
- C. Perspiration
- D. Melanin
Correct Answer: D
Rationale: Melanin is the pigment responsible for skin color and serves as a natural defense against ultraviolet (UV) rays. When the skin is exposed to UV rays, melanin production increases to absorb and dissipate the radiation, acting as a protective mechanism. This helps prevent DNA damage, reducing the risk of skin cancer and other UV-induced skin issues. Therefore, melanin is the substance that effectively shields the body from the harmful effects of UV radiation.
Which of the following characteristics of water helps explain why coastal areas experience less dramatic temperature changes during the day than more inland areas?
- A. Water's adhesive properties prevent evaporation.
- B. Water is a versatile solvent.
- C. Water has a high specific heat capacity.
- D. Water forms covalent bonds with other water molecules.
Correct Answer: C
Rationale: The correct answer is C. Water has a high specific heat capacity, meaning it can absorb and store a large amount of heat energy before its temperature rises significantly. This characteristic allows water to moderate temperature changes by absorbing heat during the day and releasing it slowly at night, resulting in less dramatic temperature fluctuations along coastal areas compared to inland areas. Water's adhesive properties (choice A) do not directly contribute to moderating temperature changes. While being a versatile solvent (choice B) is a notable property of water, it is not the primary reason for the specific temperature moderation observed in coastal areas. Water forming covalent bonds with other water molecules (choice D) is more related to its molecular structure rather than its role in temperature moderation.
Which of the following substances is excreted by the sweat glands in response to the breakdown of proteins and the formation of ammonia?
- A. Lysozymes
- B. Water
- C. Urea
- D. Sebum
Correct Answer: C
Rationale: The correct answer is Urea. Sweat glands excrete urea in response to the breakdown of proteins and the formation of ammonia. Urea is a waste product formed in the liver by the breakdown of amino acids. It is then excreted by the kidneys in urine and by sweat glands through perspiration. Urea plays a vital role in the excretory process by helping eliminate nitrogenous wastes from the body and maintaining proper physiological balance.
The triple point of a substance is the temperature and pressure at which of the substance exists as which of the following?
What is the triple point of a substance?
- A. Simultaneously in solid, liquid, and gas phases.
- B. As soil with gas and solid trapped in liquid.
- C. As a gel with solid and liquid trapped in gas.
- D. Simultaneously in solid, gel, and plasma phases.
Correct Answer: A
Rationale: The triple point of a substance refers to the specific temperature and pressure at which the substance can exist in equilibrium as solid, liquid, and gas phases simultaneously. This unique point represents the conditions under which all three phases coexist in equilibrium, allowing for phase transitions without a change in temperature or pressure. It is a crucial concept in thermodynamics and phase diagrams, illustrating the conditions where a substance can exhibit distinct phases simultaneously.
Which one of the following structures drains oxygen-depleted blood from the kidneys?
- A. Ureter
- B. Renal artery
- C. Urethra
- D. Renal vein
Correct Answer: D
Rationale: The correct answer is D, Renal vein. The renal vein is responsible for draining oxygen-depleted blood from the kidneys back to the heart for reoxygenation. The ureter carries urine from the kidneys to the bladder, the renal artery supplies oxygenated blood to the kidneys, and the urethra is the tube that carries urine from the bladder out of the body. Therefore, in the context of blood drainage from the kidneys, the renal vein is the correct choice.