Nokea
Which element has an atomic mass greater than that of sodium?
- A. Boron
- B. Oxygen
- C. Fluorine
- D. Silicon
Correct Answer: D
Rationale: Silicon has an atomic mass greater than that of sodium. The atomic mass of silicon is approximately 28.0855 u, whereas the atomic mass of sodium is approximately 22.9898 u. Therefore, silicon has a greater atomic mass compared to sodium. Boron, Oxygen, and Fluorine have atomic masses lower than sodium, making them incorrect choices in this context.
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What is the correct electron configuration for nitrogen?
- A. 1s² 2s²
- B. 1s² 2s² 2p²
- C. 1s² 2s² 2p³
- D. 1s² 2s² 2pâ´
Correct Answer: C
Rationale: The electron configuration of nitrogen is determined by its atomic number, which is 7. Nitrogen has 7 electrons. Following the order of filling orbitals, the electron configuration for nitrogen is 1s² 2s² 2p³. This means the first energy level is filled with 2 electrons in the 1s orbital, the second energy level is filled with 2 electrons in the 2s orbital, and 3 electrons in the 2p orbital. Each orbital can hold a specific number of electrons, and nitrogen, with its 7 electrons, fits this configuration. Choice A is incorrect because it does not account for all the electrons in the nitrogen atom. Choice B is incorrect as it only represents 6 electrons, not the 7 electrons in nitrogen. Choice D is incorrect as it represents 8 electrons, which is not the correct electron configuration for nitrogen.
Arsenic and silicon are examples of ___________.
- A. metals
- B. nonmetals
- C. metalloids
- D. heavy metals
Correct Answer: C
Rationale: Arsenic and silicon are both examples of metalloids. Metalloids have properties that lie between those of metals and nonmetals. They exhibit characteristics of both groups, making them versatile elements with various applications in different industries. Choice A (metals) is incorrect as arsenic and silicon do not exhibit typical metallic properties. Choice B (nonmetals) is incorrect as they do not possess all the properties of nonmetals. Choice D (heavy metals) is incorrect as heavy metals refer to a different group of elements with high atomic weights, and arsenic and silicon are not categorized as heavy metals.
What is the oxidation state of the potassium ion in the compound KCl?
- A. +1
- B. -1
- C. +2
- D. -2
Correct Answer: A
Rationale: In the compound KCl (potassium chloride), potassium is in Group 1 of the periodic table, which means it has a valence electron of 1. Chlorine is in Group 17 and gains one electron to achieve a stable electron configuration by forming an ionic bond with potassium. As a result, the potassium ion in KCl has a +1 oxidation state. Therefore, the correct answer is +1. Choices B, C, and D are incorrect as they do not reflect the oxidation state of the potassium ion in KCl.
Which substance forms hydroxide ions when placed in water?
- A. Lemon juice
- B. Battery acid
- C. Vinegar
- D. Lye
Correct Answer: D
Rationale: The correct answer is D, lye. Lye, also known as sodium hydroxide (NaOH), is a strong base that forms hydroxide ions (OH-) when placed in water. When lye dissolves in water, it dissociates into sodium ions (Na+) and hydroxide ions, making it an alkaline substance. Lemon juice, battery acid, and vinegar do not form hydroxide ions when placed in water. Lemon juice contains citric acid, battery acid contains sulfuric acid, and vinegar contains acetic acid, none of which produce hydroxide ions when dissolved in water.
What is the correct formula for calcium carbonate?
- A. CaSO₃
- B. CaCO₃
- C. Ca(OH)â‚‚
- D. CH₃OH
Correct Answer: B
Rationale: The correct formula for calcium carbonate is CaCO₃, which consists of one calcium (Ca) atom, one carbon (C) atom, and three oxygen (O) atoms. Therefore, choice B, CaCO₃, is the accurate formula for calcium carbonate. Choices A, C, and D do not represent the correct formula for calcium carbonate. Choice A, CaSO₃, is calcium sulfite, not calcium carbonate. Choice C, Ca(OH)₂, is calcium hydroxide, and choice D, CH₃OH, is methanol, none of which are correct formulas for calcium carbonate.