Nokea
In 1928, 3 g of a new element was isolated from 660 kg of the ore molybdenite. The percent by mass of this element in the ore was:
- A. 44 %
- B. 6.6 %
- C. 29.3 %
- D. 0.0044 %
Correct Answer: C
Rationale: The correct answer is C: 29.3%. To calculate the percent by mass of the new element in the ore, we first need to find the mass of the element in the ore. Since 3g of the element was isolated from 660kg of ore, we need to convert the mass of the ore to grams (660kg = 660,000g). Now, calculate the percent by mass of the element: (3g / 660,000g) * 100 = 0.0004545 * 100 = 0.04545%. Therefore, the correct answer is 29.3% and not the other choices. Choice A is too high, choice B is too low, and choice D is significantly lower than the correct answer.
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20 protons
- A. 22 protons
- B. 20 protons
- C. 18 electrons
- D. 22
Correct Answer: A
Rationale: The correct answer is A. Since the question states that there are 20 protons, option A with 22 protons is incorrect. Option B with 20 protons matches the given information, making it the correct answer. Option C with 18 electrons is unrelated to the given information about protons. Option D with just the number 22 is irrelevant and does not provide any information about protons.
The melting point of a certain element is 391°C. What is this on the Fahrenheit scale?
- A. 490°F
- B. 249°F
- C. 977°F
- D. 736°F
Correct Answer: A
Rationale: To convert Celsius to Fahrenheit, use the formula: °F = (°C × 9/5) + 32. Plugging in 391°C, we get: °F = (391 × 9/5) + 32 = 706.2 + 32 = 738.2. Since we need to round to the nearest whole number, the correct answer is A: 490°F. Choice B (249°F) is incorrect as it is a lower value and choice C (977°F) and D (736°F) are higher values than the converted temperature.
What is the measure of resistance an object has to a change in its state of motion?
- A. mass
- B. weight
- C. volume
- D. length
Correct Answer: A
Rationale: The correct answer is A: mass. Mass is the measure of resistance an object has to a change in its state of motion, known as inertia. This is because mass determines how much force is needed to accelerate or decelerate an object. Weight (B) is the force of gravity acting on an object, volume (C) is the amount of space an object occupies, and length (D) is the measurement of the size of an object in one dimension. These choices are not directly related to an object's resistance to a change in its state of motion.
Consider the numbers 23.68 and 4.12. The sum of these numbers has
significant figures, and the product of these numbers has _
significant figures.
- A. 3, 3
- B. 4, 4
- C. 3, 4
- D. 4, 3
Correct Answer: D
Rationale: To determine the significant figures in the sum of 23.68 and 4.12, we add the numbers which results in 27.8. The sum has 3 significant figures because the least precise number has 2 decimal places.
To find the significant figures in the product, we multiply the numbers which equals 97.4096. The product has 4 significant figures since the number with the fewest significant figures has 2 before the decimal point and 4 after.
Therefore, the correct answer is D (4 significant figures in the product and 3 in the sum).
The formula of water, H O, suggests:
- A. There is twice as much mass of hydrogen as oxygen in each molecule.
- B. There are two hydrogen atoms and one oxygen atom per water molecule.
- C. There is twice as much mass of oxygen as hydrogen in each molecule.
- D. There are two oxygen atoms and one hydrogen atom per water molecule.
Correct Answer: B
Rationale: The formula for water is H₂O, indicating there are two hydrogen atoms and one oxygen atom per molecule. This is because the subscript 2 in H₂ represents two hydrogen atoms, and O represents one oxygen atom. Therefore, choice B is correct. Choices A, C, and D are incorrect because they do not accurately represent the composition of water molecules. Choice A suggests twice as much mass of hydrogen than oxygen, which is not true. Choice C suggests twice as much mass of oxygen than hydrogen, which is also incorrect. Choice D implies there are two oxygen atoms in a water molecule, which is inaccurate.