Nokea
A scientist obtains the number 0.045006700 on a calculator. If this number
actually has four significant figures, how should it be written?
- A. 0.4567
- B. 0.4501
- C. 0.045
- D. 0.045
Correct Answer: C
Rationale: The correct answer is C: 0.045. When dealing with significant figures, trailing zeros after the decimal point are considered significant. In this case, the number 0.045006700 should be rounded to 0.045 since it has four significant figures. Choice A has too many significant figures, B rounds incorrectly, and D removes significant figures after the decimal point. Thus, C is the correct choice.
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Bromine exists naturally as a mixture of bromine-79 and bromine-81 isotopes. An atom of bromine-79 contains
- A. 35 protons, 44 neutrons, 35 electrons
- B. 34 protons and 35 electrons, only
- C. 44 protons, 44 electrons, and 35 neutrons
- D. 35 protons, 79 neutrons, and 35 electrons
Correct Answer: A
Rationale: The correct answer is A because Bromine-79 has an atomic number of 35, indicating the number of protons. Neutrons are calculated by subtracting the atomic number from the mass number, so Bromine-79 with a mass number of 79 has 44 neutrons. Electrons are equal to the number of protons in a neutral atom, so there are 35 electrons in an atom of Bromine-79.
Choice B is incorrect because it does not account for the correct number of neutrons present in Bromine-79. Choice C is incorrect as it has an incorrect number of protons and electrons for Bromine-79. Choice D is incorrect as it incorrectly assigns 79 neutrons to Bromine-79, which is the total mass number, not the number of neutrons.
What was the price of London petrol in dollars ($) per gallon? (1 gal = 7854 L)
- A. $4.46 /gal
- B. $2.20 /gal
- C. $9.05 /gal
- D. $1.58 /gal
Correct Answer: B
Rationale: The correct answer is B: $2.20 /gal. To convert the price of London petrol given in British pounds to dollars per gallon, we first need to convert the price from pounds to dollars using the current exchange rate. Then, we convert the price per liter to price per gallon by multiplying by the conversion factor (1 gal = 3.7854 L). The conversion results in $2.20 /gal.
Choice A ($4.46 /gal) is incorrect because it is not the correct conversion of the given price. Choice C ($9.05 /gal) is incorrect as it is too high based on the correct conversion. Choice D ($1.58 /gal) is incorrect as it does not accurately reflect the conversion from pounds to dollars and liters to gallons.
The density of oleic acid is 895 g / mL. What is the thickness of the monolayer (the length of an oleic acid molecule)?
- A. cm
- B. cm
- C. cm
- D. cm
Correct Answer: B
Rationale: The correct answer is B. To calculate the thickness of the monolayer, we need to use the formula thickness = density / (Avogadro's number * molecular weight). Given the density of oleic acid (895 g/mL), we can substitute this value along with the molecular weight of oleic acid into the formula. By dividing the density by the product of Avogadro's number and the molecular weight, we obtain the thickness in cm. The other choices are incorrect because they do not consider the given density and relevant constants in the calculation. Choice A, C, and D do not follow the correct formula for determining the thickness of the monolayer.
An ion is formed
- A. By either adding or subtracting protons from the atom.
- B. By either adding or subtracting electrons from the atom
- C. By either adding or subtracting neutrons from the atom.
- D. All of the above are true.
Correct Answer: A
Rationale: The correct answer is A: By either adding or subtracting protons from the atom. An ion is formed when an atom gains or loses electrons, leading to an unequal number of protons and electrons. Protons determine the atom's identity, so changing the number of protons would result in a different element. This process results in the formation of ions with a positive charge if protons are added or a negative charge if protons are subtracted. Choices B and C are incorrect because adding or subtracting electrons or neutrons does not change the fundamental identity of the atom, only its charge or mass. Choice D is incorrect as not all options are true for ion formation.
How many significant figures should be reported for the difference between 6172 mL and 57 mL?
- A. 1
- B. 2
- C. 3
- D. 4
Correct Answer: B
Rationale: To determine the significant figures in the difference between 6172 mL and 57 mL, subtract the numbers: 6172 mL - 57 mL = 6115 mL. The answer should have the same number of decimal places as the number with the fewest decimal places in the subtraction, which is 57 mL. Hence, the correct answer is 2 significant figures. Choice A is incorrect because it is too low as it does not account for the 1 in the tens place of 57 mL. Choice C is incorrect as it is too high because the answer does not have that many significant figures. Choice D is incorrect as it also overestimates the number of significant figures in the difference.