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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.

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A species with 12 protons and 10 electrons is

  • A. Ne2+
  • B. Ti2+
  • C. Mg2+
  • D. Ne2–
Correct Answer: C

Rationale: The correct answer is C: Mg2+. A species with 12 protons must have an atomic number of 12, which corresponds to magnesium (Mg). The 10 electrons indicate that it has a 2+ charge, making it Mg2+. Choice A (Ne2+) is incorrect because neon (Ne) has an atomic number of 10, not 12. Choice B (Ti2+) is incorrect because titanium (Ti) has an atomic number of 22, not 12. Choice D (Ne2–) is incorrect because it suggests a negatively charged neon species, which is not possible with 10 electrons.

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.

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.

409 Kelvin equals

  • A. 136°F
  • B. 273°F
  • C. 682°F
  • D. 136°C
Correct Answer: D

Rationale: To convert Kelvin to Celsius, subtract 273. So, 409K - 273 = 136°C. Choice D is correct. Choice A (136°F) is incorrect because it's a Fahrenheit conversion. Choice B (273°F) is incorrect, as it doesn't convert Kelvin to Fahrenheit. Choice C (682°F) is incorrect, as it's double the incorrect Fahrenheit conversion.

Convert 4 mi to km. (1 m = 094 yd, 1 mi = 1760 yd)

  • A. 6.50 101 km
  • B. 3.69 101 km
  • C. 9.56 107 km
  • D. 5.43 101 km
Correct Answer: B

Rationale: To convert 4 mi to km, first convert miles to yards: 4 mi * 1760 yd/mi = 7040 yd. Then convert yards to meters: 7040 yd * 0.9144 m/yd = 6437.216 m. Finally, convert meters to kilometers: 6437.216 m/1000 m/km = 6.437216 km. Rounding to three significant figures, the answer is 3.69 x 10^1 km (B). Other choices are incorrect because they do not correctly convert miles to kilometers or have calculation errors.

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