Nokea
What type of chemical reaction is represented by AB → A + B?
- A. Synthesis
- B. Decomposition
- C. Single replacement
- D. Double replacement
Correct Answer: B
Rationale: The chemical equation AB → A + B represents a decomposition reaction. In a decomposition reaction, a single compound breaks down into two or more simpler substances. In this specific reaction, compound AB is decomposed into its elements, A and B, making it a decomposition reaction. Choice A, Synthesis, involves the combination of two or more substances to form a more complex product, which is not the case here. Choices C and D, Single replacement and Double replacement, involve the exchange of ions between compounds or elements, which is not happening in the given reaction.
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What is the correct electron configuration for magnesium?
- A. 1s² 2s²
- B. 1s² 2s² 2pâ¶
- C. 1s² 2s² 2pⶠ3s²
- D. 1s² 2s² 2pⶠ3s² 3p¹
Correct Answer: C
Rationale: The electron configuration of an element is determined by following the Aufbau principle, which states that electrons fill orbitals starting from the lowest energy level. Magnesium has an atomic number of 12, meaning it has 12 electrons. The electron configuration of magnesium fills the 1s, 2s, 2p, and 3s orbitals to accommodate all 12 electrons. Therefore, the correct electron configuration for magnesium is 1s² 2s² 2pⶠ3s². Choice A is incorrect as it only includes 4 electrons and stops at the 2s orbital. Choice B is incorrect as it includes 8 electrons and stops at the 2p orbital. Choice D is incorrect as it includes 13 electrons and extends to the 3p orbital, which is beyond the actual electron configuration of magnesium.
What is the molarity of a solution containing 45 moles of NaCl in 4 liters?
- A. 0.11 M NaCl
- B. 0.45 M NaCl
- C. 1.8 M NaCl
- D. 8.9 M NaCl
Correct Answer: A
Rationale: To calculate the molarity of a solution, you use the formula: Molarity (M) = moles of solute / liters of solution. In this case, M = 45 moles / 4 L = 11.25 M. The correct answer is 0.11 M NaCl. Choice B is incorrect as it doesn't match the calculated value. Choice C is also incorrect as it is significantly higher than the correct molarity. Choice D is incorrect as it is excessively high compared to the calculated value.
What is the name of the compound CH₃-CH₂-CH₂-CH₃?
- A. Cyclobutane
- B. Butane
- C. Butene
- D. Butyne
Correct Answer: B
Rationale: The compound CH₃-CH₂-CH₂-CH₃ is named butane. Butane is a straight-chain alkane comprising four carbon atoms connected by single bonds. The prefix 'but-' denotes the presence of four carbon atoms, while the suffix '-ane' indicates it is an alkane with single bonds between the carbon atoms. Choice A, Cyclobutane, is incorrect as it refers to a cyclic hydrocarbon with four carbon atoms in a ring structure. Choice C, Butene, is incorrect because it is an alkene with a double bond between two carbon atoms, not a saturated hydrocarbon like butane. Choice D, Butyne, is also incorrect as it is an alkyne with a triple bond between two carbon atoms, unlike the single bonds in butane.
What is the energy required to remove the outermost electron from an atom called?
- A. covalent bonding
- B. electronegativity
- C. atomic radius
- D. ionization energy
Correct Answer: D
Rationale: Ionization energy is the energy needed to remove the outermost electron from an atom, resulting in the formation of a positively charged ion. The higher the ionization energy, the more difficult it is to extract an electron. Electronegativity, however, measures an atom's ability to attract shared electrons in a chemical bond. Atomic radius refers to the distance from the nucleus to the outermost electron. Covalent bonding involves sharing electron pairs between atoms to create a stable bond. Therefore, the correct answer is ionization energy as it specifically relates to the energy needed to remove an electron from an atom.
Which of these elements has the greatest atomic mass?
- A. Au
- B. Ba
- C. I
- D. W
Correct Answer: D
Rationale: Among the elements listed, Tungsten (W) has the greatest atomic mass. The atomic mass of Tungsten is approximately 183.84 atomic mass units (amu), while the atomic masses of the other elements listed are as follows: Gold (Au) is around 196.97 amu, Barium (Ba) is approximately 137.33 amu, and Iodine (I) is about 126.90 amu. Therefore, Tungsten (W) has the greatest atomic mass out of the given elements. Gold (Au) has a higher atomic mass than Barium (Ba) and Iodine (I), making choices A, B, and C incorrect.