Question 1

Which of the following statements best describes the law of conservation of mass as established by Antoine Lavoisier?
Correct answer: The total mass of reactants and products remains constant during a chemical reaction.

Accepted Answer

The total mass of reactants and products remains constant during a chemical reaction.

Question 2

A forensic scientist is analyzing tooth enamel to estimate a person's year of birth. Which isotope is most relevant for this analysis, and why?
Correct answer: Carbon-14, because its atmospheric levels changed due to nuclear testing and can be traced in biological samples.

Accepted Answer

Carbon-14, because its atmospheric levels changed due to nuclear testing and can be traced in biological samples.

Question 3

Which of the following changes would result in a different element being formed?
Correct answer: Changing the number of protons in the nucleus.

Accepted Answer

Changing the number of protons in the nucleus.

Question 4

A sample of element X contains two naturally occurring isotopes: X-29 (mass = 29.0 amu, abundance = 60%) and X-30 (mass = 30.0 amu, abundance = 40%). What is the average atomic mass of element X?
Correct answer: 29.4 amu

Accepted Answer

29.4 amu

Question 5

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 6

Which experiment or observation provided the strongest evidence that atoms are mostly empty space?
Correct answer: The deflection of alpha particles in Rutherford's gold foil experiment.

Accepted Answer

The deflection of alpha particles in Rutherford's gold foil experiment.

Question 7

A neutral atom of element Y has 17 protons and 18 neutrons. What is its mass number and atomic number?
Correct answer: Mass number = 35, atomic number = 17

Accepted Answer

Mass number = 35, atomic number = 17

Question 8

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 a weighted average of the masses of all naturally occurring isotopes of chlorine.

Accepted Answer

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

Question 9

Which of the following statements is inconsistent with Dalton’s atomic theory as originally proposed?
Correct answer: Atoms can be divided into smaller subatomic particles.

Accepted Answer

Atoms can be divided into smaller subatomic particles.

Question 10

A mass spectrometer is used to analyze a sample of magnesium. Which property allows the instrument to separate different isotopes of magnesium?
Correct answer: Their different masses.

Accepted Answer

Their different masses.

Question 11

A neutral atom has 15 electrons and 16 neutrons. Which element is it, and what is its mass number?
Correct answer: Phosphorus, mass number 31

Accepted Answer

Phosphorus, mass number 31

Question 12

Which of the following real-world applications relies on the law of constant composition?
Correct answer: Determining the purity of a pharmaceutical compound by analyzing its elemental ratios.

Accepted Answer

Determining the purity of a pharmaceutical compound by analyzing its elemental ratios.

Question 13

If an atom has a charge of +2, 20 protons, and 18 electrons, how many neutrons does it have if its mass number is 40?
Correct answer: 20

Accepted Answer

20

Question 14

Which of the following best describes the difference between a cation and an anion?
Correct answer: A cation has more protons than electrons, while an anion has more electrons than protons.

Accepted Answer

A cation has more protons than electrons, while an anion has more electrons than protons.

Question 15

Which of the following scenarios would NOT result in the formation of an isotope?
Correct answer: Adding or removing protons from the nucleus.

Accepted Answer

Adding or removing protons from the nucleus.

Question 16

A sample contains 70% isotope A (mass = 10 amu) and 30% isotope B (mass = 11 amu). What is the average atomic mass of the sample?
Correct answer: 10.3 amu

Accepted Answer

10.3 amu

Question 17

Which of the following best explains why isotopic analysis is useful in archaeology?
Correct answer: It allows scientists to date artifacts by measuring the ratios of specific isotopes.

Accepted Answer

It allows scientists to date artifacts by measuring the ratios of specific isotopes.

Question 18

Which of the following is a direct consequence of the law of definite proportions?
Correct answer: A given compound always contains the same elements in the same ratio by mass.

Accepted Answer

A given compound always contains the same elements in the same ratio by mass.

Question 19

Which of the following best describes the relationship between atomic number, mass number, and isotopes?
Correct answer: Isotopes have the same atomic number but different mass numbers.

Accepted Answer

Isotopes have the same atomic number but different mass numbers.

Question 20

Which of the following statements about the structure of the atom is correct?
Correct answer: Most of the mass of an atom is concentrated in its nucleus.

Accepted Answer

Most of the mass of an atom is concentrated in its nucleus.

Atomic Structure and Isotopes: Foundations and Applications

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