Nokea
Among the following molecules, which one contains the fewest covalent bonds?
- A. Water molecule (H2O)
- B. Methane molecule (CH4)
- C. Chlorine molecule (Cl2)
- D. Ammonia molecule (NH3)
Correct Answer: C
Rationale: The correct answer is C. The chlorine molecule (Cl2) contains the fewest covalent bonds as it consists of two chlorine atoms sharing a single covalent bond. Water (H2O), methane (CH4), and ammonia (NH3) involve multiple atoms bonded together, leading to more covalent bonds compared to the chlorine molecule. Hence, among the options provided, the chlorine molecule has the least number of covalent bonds.
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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.
Which of the following chemicals is released by one type of immune cell to directly activate another immune cell?
- A. lysozymes
- B. cytokines
- C. perforin
- D. granzymes
Correct Answer: B
Rationale: The correct answer is B: cytokines. Cytokines are signaling molecules released by immune cells to regulate the immune response. They play a crucial role in coordinating and communicating between different immune cells. By releasing cytokines, immune cells can directly activate other immune cells, enhancing the immune response. Lysozymes are enzymes that break down bacterial cell walls, perforin is a protein involved in cell-mediated immune responses, and granzymes are enzymes that induce apoptosis in target cells, mainly used by cytotoxic T cells and natural killer cells, not for directly activating other immune cells.
A student makes a solution that simulates stomach acid. Which of the following would be true of this solution, compared to distilled water?
- A. It has a higher pH.
- B. It has more hydrogen ions.
- C. It contains more hydroxyl ions.
- D. It has more hydroxyl ions.
Correct Answer: B
Rationale: The correct answer is B. A solution that simulates stomach acid is acidic, which means it has a higher concentration of hydrogen ions compared to distilled water, which is neutral. Stomach acid is characterized by its high hydrogen ion concentration, which is responsible for its acidic nature. Hydroxyl ions are associated with bases, not acids, so options C and D are incorrect. Option A is incorrect as well because stomach acid would have a lower pH compared to distilled water due to its high acidity.
Which of the following statements best describes the function of a buffer?
- A. It permanently binds hydrogen ions.
- B. It causes the pH of a solution to become neutral.
- C. It decreases the pH of the solution.
- D. It enables resistance to a change in pH.
Correct Answer: D
Rationale: The correct answer is D: 'It enables resistance to a change in pH.' Buffers function by resisting changes in pH when small amounts of acid or base are added to a solution, thereby maintaining a stable pH. Option A is incorrect because buffers do not permanently bind hydrogen ions; they can release or absorb them as needed to maintain pH. Option B is incorrect because buffers do not necessarily cause a solution's pH to become neutral; they stabilize the pH at a specific value. Option C is incorrect; buffers can increase or decrease pH depending on the conditions to maintain stability. Therefore, the best description of a buffer's function is its ability to resist changes in pH.
Which of the following properties does soap, an emulsifier, have that make it useful for washing dirt off one's hands with water?
- A. Soap's dual polar and nonpolar nature helps bond oil and water.
- B. Soap's acidity causes grime to precipitate into the water.
- C. Soap's rough texture physically scours grime off surfaces.
- D. Soap's enzymatic action helps to dissolve grime into smaller particles.
Correct Answer: A
Rationale: Soap acts as an emulsifier due to its dual polar (hydrophilic) and nonpolar (hydrophobic) nature, allowing it to effectively bond oil and water, making option A the correct choic