Nokea
Identify the element with the electron configuration: 1s2 2s2 2p6 3s2 3p6. To which group and period does this element belong?
- A. Group 16, Period 3
- B. Group 14, Period 3
- C. Group 18, Period 3
- D. Group 17, Period 2
Correct Answer: C
Rationale: The given electron configuration matches that of Argon, an element found in Group 18 of the periodic table. This element is in the third period, as indicated by the highest energy level (n=3) where electrons are present. Therefore, the correct answer is Group 18, Period 3. Choice A (Group 16, Period 3) corresponds to sulfur, not the given electron configuration. Choice B (Group 14, Period 3) corresponds to silicon, not the given electron configuration. Choice D (Group 17, Period 2) corresponds to chlorine, which is in Period 3 but not in Group 18, making it incorrect for the given electron configuration.
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Which property of a wave remains constant when it crosses a boundary between two different media?
- A. Frequency
- B. Wavelength
- C. Amplitude
- D. Speed
Correct Answer: D
Rationale: When a wave crosses a boundary between two different media, its speed is the property that remains constant. This is due to the principle of conservation of energy. While the frequency and wavelength of a wave may change as it moves from one medium to another, the speed of the wave remains constant. This phenomenon is a result of the wave adjusting its frequency and wavelength to maintain a consistent speed in different media. Therefore, choices A, B, and C are incorrect. Frequency and wavelength may change when a wave moves across media, and amplitude may also be affected by the medium, but the speed of the wave will remain constant.
In the reaction 2Na + 2H2O → 2NaOH + H2, what is the limiting reactant when 3 moles of sodium react with 2 moles of water?
- A. Na
- B. H2O
- C. NaOH
- D. H2
Correct Answer: A
Rationale: The balanced chemical equation indicates that 2 moles of sodium react with 2 moles of water to yield 2 moles of sodium hydroxide and 1 mole of hydrogen gas. When 3 moles of sodium react with only 2 moles of water, sodium becomes the limiting reactant as it is present in excess compared to the available water molecules. This situation arises because not all sodium atoms can fully react with the limited amount of water, resulting in sodium being the limiting reactant in this specific case. Choice B (H2O), choice C (NaOH), and choice D (H2) are incorrect as they are not the limiting reactant in the given reaction scenario.
If you compare a 1 M solution of NaCl to a 1 M solution of glucose (C6H12O6) in water, which solution would have the higher boiling point?
- A. The NaCl solution
- B. The glucose solution
- C. They would have the same boiling point
- D. It depends on the temperature
Correct Answer: A
Rationale: 1. Boiling point elevation: When a solute is added to a solvent, it raises the boiling point of the solution compared to the pure solvent. This phenomenon is known as boiling point elevation.
2. Van't Hoff factor: The extent of boiling point elevation depends on the number of particles the solute dissociates into in the solution. NaCl dissociates into two ions (Na+ and Cl-) in water, while glucose does not dissociate into ions. Therefore, NaCl has a higher Van't Hoff factor than glucose.
3. Colligative properties: Boiling point elevation is a colligative property, meaning it depends on the concentration of the solute particles, not the identity of the solute. Since both NaCl and glucose are 1 M solutions, the NaCl solution will have a higher boiling point due to its higher Van't Hoff factor.
4. Conclusion: The NaCl solution
Why is biodiversity important for healthy ecosystems?
- A. Increases stability and resilience to disturbances
- B. Provides stability and resilience to disturbances
- C. Slows down nutrient cycling
- D. Reduces the number of decomposers
Correct Answer: B
Rationale: Biodiversity refers to the variety of living organisms in a particular area. A diverse ecosystem is better able to withstand and recover from disturbances such as natural disasters, climate change, or human impacts. This is because different species play unique roles in the ecosystem, and a higher level of biodiversity means there are more species available to fulfill these roles. For example, if one species is negatively affected by a disturbance, other species may be able to compensate for its loss, maintaining the overall functioning of the ecosystem. Therefore, biodiversity provides stability and resilience to disturbances, making ecosystems healthier and more sustainable. Choice A is incorrect because biodiversity doesn't increase competition for resources but rather helps in maintaining a balance within the ecosystem. Choice C is incorrect as biodiversity does not slow down nutrient cycling; in fact, it enhances nutrient cycling by ensuring a variety of species involved in the process. Choice D is incorrect as biodiversity does not reduce the number of decomposers but instead supports a diverse community of decomposers that are essential for nutrient recycling in ecosystems.
What is the process of breaking down glucose into pyruvate called?
- A. Glycolysis
- B. Gluconeogenesis
- C. Krebs cycle
- D. Oxidative phosphorylation
Correct Answer: A
Rationale: A) Glycolysis is the process of breaking down glucose into pyruvate. This occurs in the cytoplasm of cells and is the first step in cellular respiration.
B) Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate sources, such as amino acids or glycerol, and is the opposite of glycolysis.
C) The Krebs cycle, also known as the citric acid cycle, is a series of chemical reactions that occur in the mitochondria and is involved in the oxidation of acetyl-CoA to produce ATP and other energy carriers.
D) Oxidative phosphorylation is the final stage of cellular respiration where ATP is produced through the transfer of electrons in the electron transport chain.