Nokea
An uncharged atom has an electron configuration of 1s² 2s² 2pⶠ3s² and a mass number of 14. How many protons does it have?
- A. 14
- B. 6
- C. 8
- D. 12
Correct Answer: B
Rationale: The number of protons in an atom is determined by the atomic number, which is equal to the number of protons in the nucleus. The electron configuration given corresponds to carbon (C) with 6 protons. The atomic number of an element is the same as the number of protons in its nucleus, so in this case, the atom has 6 protons. Choices A, C, and D are incorrect because they do not correspond to the correct number of protons for an atom with the given electron configuration and mass number. Therefore, option B, 6 protons, is the correct answer.
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What is the scientific name for the common housefly?
- A. Musca domestica
- B. Drosophila melanogaster
- C. Apis mellifera
- D. Anopheles gambiae
Correct Answer: A
Rationale: Musca domestica is the scientific name for the common housefly. This species is known for being a common pest found in and around human habitations. Drosophila melanogaster (option B) is a species of fruit fly commonly used in genetic research. Apis mellifera (option C) is the scientific name for the western honeybee. Anopheles gambiae (option D) is a species of mosquito known for being a vector of malaria.
What is the name of the structure that packages DNA in eukaryotic cells?
- A. Nucleosome
- B. Chromatin
- C. Histone
- D. Centromere
Correct Answer: A
Rationale: - A nucleosome is the basic structural unit of DNA packaging in eukaryotic cells. It consists of DNA wrapped around a core of histone proteins.
- Chromatin refers to the complex of DNA and proteins found in the nucleus of a eukaryotic cell, including nucleosomes.
- Histones are the proteins around which DNA is wrapped to form nucleosomes.
- Centromere is a region of a chromosome where the two sister chromatids are joined and to which spindle fibers attach during cell division.
When sodium hydroxide (NaOH) reacts with hydrochloric acid (HCl), the resulting product is:
- A. Hydrogen gas and sodium chloride (NaCl)
- B. Chlorine gas and sodium oxide (Na2O)
- C. Sodium metal (Na) and water (H2O)
- D. No reaction occurs.
Correct Answer: A
Rationale: When sodium hydroxide (NaOH) reacts with hydrochloric acid (HCl), a neutralization reaction occurs. The products of this reaction are water (H2O) and a salt, which is sodium chloride (NaCl). The chemical equation for this reaction is: NaOH + HCl -> NaCl + H2O. Choice B is incorrect because chlorine gas and sodium oxide are not the products of this reaction. Choice C is incorrect as sodium metal and water are not the products formed in this neutralization reaction. Choice D is incorrect because a reaction does occur between NaOH and HCl, resulting in the formation of NaCl and H2O. Therefore, the correct answer is A: Hydrogen gas and sodium chloride (NaCl).
What potential consequences can chromosomal nondisjunction have on offspring?
- A. Down syndrome, caused by an extra copy of chromosome 21.
- B. Turner syndrome, characterized by the absence of one X chromosome in females.
- C. Klinefelter syndrome, featuring one or more extra X chromosomes in males.
- D. All of the above.
Correct Answer: D
Rationale: - Chromosomal nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division, leading to an abnormal number of chromosomes in the resulting cells.
- Down syndrome is caused by an extra copy of chromosome 21, resulting from nondisjunction during meiosis. Individuals with Down syndrome have three copies of chromosome 21 instead of the usual two.
- Turner syndrome is characterized by the absence of one X chromosome in females, leading to a variety of physical and developmental features.
- Klinefelter syndrome features one or more extra X chromosomes in males, typically resulting in infertility and other physical characteristics.
Therefore, chromosomal nondisjunction can lead to various genetic disorders such as Down syndrome, Turner syndrome, and Klinefelter syndrome, making option D the correct answer.
What property of a wave determines its speed in a given medium?
- A. Amplitude
- B. Wavelength
- C. Frequency
- D. Medium's properties
Correct Answer: D
Rationale: The speed of a wave in a given medium is determined by the properties of that medium, such as its density and elasticity. While amplitude, wavelength, and frequency are important characteristics of a wave, they do not directly impact its speed in a specific medium. Amplitude refers to the maximum displacement of particles in a wave, wavelength is the distance between two successive points in a wave that are in phase, and frequency is the number of complete oscillations a wave makes in a given time. However, these properties do not dictate the speed of a wave in a particular medium. Therefore, the correct answer is the medium's properties.