Nokea
The element rhenium (Re) exists as two stable isotopes and 18 unstable isotopes. Rhenium-185 has in its nucleus
- A. 75 protons, 75 neutrons
- B. 75 protons, 130 neutrons
- C. 130 protons, 75 neutrons
- D. 75 protons, 110 neutrons
Correct Answer: A
Rationale: The correct answer A is determined by knowing that the atomic number of rhenium is 75. Since the element is rhenium-185, the sum of protons and neutrons must equal 185. As the atomic number is 75, the number of protons is 75. Therefore, the number of neutrons is 185 - 75 = 110. Thus, rhenium-185 has 75 protons and 110 neutrons. Choices B, C, and D are incorrect as they do not adhere to the correct number of protons and neutrons in the nucleus of rhenium-185.
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The statement “The total mass of materials is not affected by a chemical change in thosematerials” is called a(n)
- A. observation
- B. measuremen t
- C. theory
- D. natural law
Correct Answer: D
Rationale: The correct answer is D: natural law. A natural law describes a consistent pattern or behavior in the natural world, such as the conservation of mass in a chemical reaction. This principle states that the total mass of materials before and after a chemical change remains constant. Observations (A) are factual statements based on data, measurements (B) involve quantifying properties, and theories (C) are explanations based on evidence, but none specifically address the consistent behavior of mass in chemical changes as a natural law does.
Convert 4 lb to g. (1 lb = 6 g)
- A. 7.58 10 2 g
- B. 1.56 103 g
- C. 7.58 104 g
- D. 1.56 102 g
Correct Answer: C
Rationale: To convert 4 lb to g, we use the conversion factor provided: 1 lb = 6 g.
1. Multiply 4 lb by 6 g/lb: 4 lb * 6 g/lb = 24 g.
2. Since the question asks for the answer in grams, the correct conversion is 24 g.
Therefore, the correct answer is C (7.58 x 10^4 g).
Other choices are incorrect because they do not correctly apply the conversion factor or provide the accurate conversion from pounds to grams.
Which statement is not correct?
- A. The mass of an alpha particle is 7300 times that of the electron.
- B. An alpha particle has a 2+ charge.
- C. Three types of radioactive emission are gamma rays, beta rays, and alpha particles.
- D. A gamma ray is high-energy light.
Correct Answer: D
Rationale: The correct answer is D because gamma rays are not light but a form of electromagnetic radiation with high energy. Gamma rays have no charge and are produced from the nucleus. Choice A is correct as an alpha particle is heavier than an electron. Choice B is correct as an alpha particle has a 2+ charge. Choice C is correct as these are types of radioactive emissions.
During a physics experiment, an electron is accelerated to 93 percent of the speed of light. What is the speed of the electron in miles per hour? (speed of light = 00 108 m/s, 1 km = 6214 mi)
- A. 2.8 108 mi/h
- B. 6.2 1011 mi/h
- C. 6.7 108 mi/h
- D. 1.0 107 mi/h
Correct Answer: C
Rationale: The correct answer is C: 6.7 x 10^8 mi/h. To calculate the speed of the electron in miles per hour, we first convert the speed of light from m/s to mi/h using the conversion factor 1 km = 6214 mi. The speed of light is approximately 6.71 x 10^8 mi/h. Since the electron is at 93% of the speed of light, we multiply the speed of light by 0.93 to get the speed of the electron, which is approximately 6.25 x 10^8 mi/h. The closest choice is C: 6.7 x 10^8 mi/h.
Choice A: 2.8 x 10^8 mi/h - This is incorrect as it is too low compared to the calculated speed.
Choice B: 6.2 x 10^11 mi/h - This is incorrect as it is too high compared to the calculated speed.
Choice
Convert 2751.4 g to mg.
- A. 2.7514 mg
- B. 27.514 mg
- C. 275.14 mg
- D. 2.7514 103 mg
Correct Answer: C
Rationale: To convert grams to milligrams, you multiply by 1000. So, 2751.4 g * 1000 = 2751.4 mg. Therefore, choice C (275.14 mg) is correct. Choice A is incorrect as it incorrectly moves the decimal point. Choice B is incorrect as it doesn't account for the conversion factor. Choice D is incorrect as it incorrectly uses scientific notation.