Question 1

Which of the following best describes the Law of Definite Proportions as established by Proust?
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 forensic scientist uses 14C isotope ratios in tooth enamel to estimate a person's year of birth. Which property of isotopes makes this possible?
Correct answer: Isotopes of an element have different numbers of neutrons, allowing for radioactive decay measurements.

Accepted Answer

Isotopes of an element have different numbers of neutrons, allowing for radioactive decay measurements.

Question 3

Which statement about Dalton’s Atomic Theory is NOT consistent with modern atomic theory?
Correct answer: Atoms of the same element are identical in mass and properties.

Accepted Answer

Atoms of the same element are identical in mass and properties.

Question 4

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 5

Which experiment or observation provided the strongest evidence that most of the mass of an atom is concentrated in a small, dense nucleus?
Correct answer: The gold foil experiment by Rutherford.

Accepted Answer

The gold foil experiment by Rutherford.

Question 6

A neutral atom of element X has 17 protons and 18 neutrons. Which of the following is correct?
Correct answer: The atomic number is 17 and the mass number is 35.

Accepted Answer

The atomic number is 17 and the mass number is 35.

Question 7

Which of the following best explains why the atomic mass of chlorine listed on the periodic table is not a whole number?
Correct answer: It is the average of the masses of all naturally occurring isotopes of chlorine, weighted by their abundance.

Accepted Answer

It is the average of the masses of all naturally occurring isotopes of chlorine, weighted by their abundance.

Question 8

Which of the following statements about subatomic particles is correct?
Correct answer: Protons and neutrons are found in the nucleus, while electrons are found outside the nucleus.

Accepted Answer

Protons and neutrons are found in the nucleus, while electrons are found outside the nucleus.

Question 9

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 10

Which scenario best illustrates the Law of Conservation of Mass?
Correct answer: A 5 g piece of magnesium reacts with 4 g of oxygen to form 9 g of magnesium oxide.

Accepted Answer

A 5 g piece of magnesium reacts with 4 g of oxygen to form 9 g of magnesium oxide.

Question 11

Which of the following is a correct statement about isotopes?
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 12

A certain element has two naturally occurring isotopes: 10X (mass = 10.01 u, abundance = 19.9%) and 11X (mass = 11.01 u, abundance = 80.1%). What is the average atomic mass of element X?
Correct answer: 10.81 u

Accepted Answer

10.81 u

Question 13

Which of the following best explains why most of the volume of an atom is empty space?
Correct answer: Electrons are much smaller than protons and neutrons and occupy regions far from the nucleus.

Accepted Answer

Electrons are much smaller than protons and neutrons and occupy regions far from the nucleus.

Question 14

Which of the following would result in a positively charged ion (cation)?
Correct answer: An atom loses electrons.

Accepted Answer

An atom loses electrons.

Question 15

Which of the following is a real-world application of the concept of isotopes?
Correct answer: Using 14C to date archaeological artifacts.

Accepted Answer

Using 14C to date archaeological artifacts.

Question 16

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

Accepted Answer

Atomic number is the number of protons; mass number is the sum of protons and neutrons.

Question 17

Which of the following would be considered a violation of Dalton’s original atomic theory, based on modern understanding?
Correct answer: Atoms can be divided into subatomic particles.

Accepted Answer

Atoms can be divided into subatomic particles.

Question 18

A sample contains 100 atoms of element Y: 60 atoms have a mass of 24 u, 25 atoms have a mass of 25 u, and 15 atoms have a mass of 26 u. What is the average atomic mass of element Y?
Correct answer: 24.55 u

Accepted Answer

24.55 u

Question 19

Which of the following best explains why mass spectrometry is a valuable tool in forensic science?
Correct answer: It can identify the isotopic composition of a sample, helping to trace its origin.

Accepted Answer

It can identify the isotopic composition of a sample, helping to trace its origin.

Atomic Structure and Isotopes: Foundations and Applications

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