Question 1

Which of the following statements best describes the Law of Definite Proportions?
Correct answer: A compound always contains the same elements in the same proportion by mass.

Accepted Answer

A compound always contains the same elements in the same proportion by mass.

Question 2

A sample of gallium contains two naturally occurring isotopes: 69Ga (mass = 68.9256 u, abundance = 60.1%) and 71Ga (mass = 70.9247 u, abundance = 39.9%). What is the average atomic mass of gallium?
Correct answer: 69.72 u

Accepted Answer

69.72 u

Question 3

Which of the following discoveries led to the revision of Dalton’s postulate that atoms are indivisible?
Correct answer: The discovery of subatomic particles such as electrons, protons, and neutrons.

Accepted Answer

The discovery of subatomic particles such as electrons, protons, and neutrons.

Question 4

A neutral atom of phosphorus has an atomic number of 15 and a mass number of 31. How many neutrons does it contain?
Correct answer: 16

Accepted Answer

16

Question 5

Which real-world application relies on the use of isotopes for determining the age of biological samples?
Correct answer: Radiocarbon dating using 14C.

Accepted Answer

Radiocarbon dating using 14C.

Question 6

A mass spectrometer separates isotopes of an element based on which property?
Correct answer: Their mass-to-charge ratio.

Accepted Answer

Their mass-to-charge ratio.

Question 7

Which statement about isotopes is correct?
Correct answer: Isotopes of an element have the same number of protons but different numbers of neutrons.

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 8

If an atom has 17 protons, 18 neutrons, and 18 electrons, what is its net charge and which element is it?
Correct answer: Net charge: -1, Element: Chlorine

Accepted Answer

Net charge: -1, Element: Chlorine

Question 9

Which of the following best explains why the atomic mass of an element on the periodic table is rarely a whole number?
Correct answer: It is a weighted average of the masses of all naturally occurring isotopes.

Accepted Answer

It is a weighted average of the masses of all naturally occurring isotopes.

Question 10

Which of the following scenarios would violate the Law of Conservation of Mass?
Correct answer: A chemical reaction in which the total mass of products is less than the total mass of reactants.

Accepted Answer

A chemical reaction in which the total mass of products is less than the total mass of reactants.

Question 11

Which statement about the structure of the atom is supported by modern atomic theory?
Correct answer: Most of the atom's mass is concentrated in a tiny, dense nucleus.

Accepted Answer

Most of the atom's mass is concentrated in a tiny, dense nucleus.

Question 12

A sample of silicon contains 92.2% 28Si (mass = 27.977 u), 4.7% 29Si (mass = 28.976 u), and 3.1% 30Si (mass = 29.974 u). What is the average atomic mass of silicon? (Round to two decimal places.)
Correct answer: 28.09 u

Accepted Answer

28.09 u

Question 13

Which of the following is NOT a postulate of Dalton’s Atomic Theory?
Correct answer: Atoms can be subdivided into protons, neutrons, and electrons.

Accepted Answer

Atoms can be subdivided into protons, neutrons, and electrons.

Question 14

A forensic scientist uses mass spectrometry to analyze a sample and finds two peaks corresponding to isotopes with masses 10 u and 11 u, with relative abundances of 80% and 20%, respectively. What is the average atomic mass of the element?
Correct answer: 10.2 u

Accepted Answer

10.2 u

Question 15

Which of the following best explains why changing the number of protons in an atom changes the element?
Correct answer: The number of protons determines the atomic number, which defines the element.

Accepted Answer

The number of protons determines the atomic number, which defines the element.

Question 16

Which of the following is a real-world example of how isotopes are used in medicine?
Correct answer: Radioisotopes are used as tracers in diagnostic imaging.

Accepted Answer

Radioisotopes are used as tracers in diagnostic imaging.

Question 17

Which of the following best describes the difference between mass number and atomic number?
Correct answer: Mass number is the total number of protons and neutrons; atomic number is the number of protons.

Accepted Answer

Mass number is the total number of protons and neutrons; atomic number is the number of protons.

Question 18

A scientist finds that a sample of an unknown element contains atoms with 20 protons and 22 neutrons. What is the correct notation for this isotope?
Correct answer: 42Ca

Accepted Answer

42Ca

Question 19

Which of the following best explains why most of the volume of an atom is empty space?
Correct answer: Electrons occupy regions far from the tiny, dense nucleus.

Accepted Answer

Electrons occupy regions far from the tiny, dense nucleus.

Atomic Structure and Isotopes: Foundations and Applications

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