MCQs — Atomic Structure

Practice questions for Chemistry.

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Question 101

Chlorine naturally occurs mainly as two isotopes, chlorine-35 and chlorine-37, both of which have the same:

A. Mass number

B. Atomic number (number of protons)

C. Number of neutrons

D. Relative atomic mass

Question 102

Which isotope of chlorine is more abundant in nature?

A. Chlorine-37

B. Both are equally abundant

C. Neither occurs naturally

D. Chlorine-35

Question 103

Chlorine has an atomic number of 17. How many neutrons are present in an atom of chlorine-37?

A. 20

B. 17

C. 37

D. 54

Question 104

Why does the relative atomic mass of chlorine listed on the periodic table (about 35.5) not exactly match either chlorine-35 or chlorine-37?

A. Chlorine has no naturally occurring isotopes

B. The periodic table only lists the least abundant isotope

C. It is a weighted average based on the relative abundance of both naturally occurring isotopes

D. Relative atomic mass ignores isotopic composition entirely

Question 105

Which of the following is a naturally occurring isotope of uranium used mainly for nuclear reactors and weapons due to its ability to sustain a chain reaction?

A. Uranium-235

B. Uranium-238

C. Uranium-234

D. Uranium-232

Question 106

The most abundant naturally occurring isotope of uranium is:

A. Uranium-235

B. Uranium-234

C. Uranium-236

D. Uranium-238

Question 107

Uranium isotopes are radioactive, meaning their nuclei are unstable and undergo:

A. No change at all over time

B. Only chemical reactions, never nuclear changes

C. Radioactive decay, releasing radiation over time

D. Permanent fusion with other elements

Question 108

Why is uranium-235, rather than uranium-238, the isotope typically used in most nuclear reactors?

A. Uranium-238 does not exist in nature

B. Uranium-235 is more easily split (fissile) to sustain a controlled nuclear chain reaction

C. Uranium-235 is not radioactive at all

D. Uranium-238 is more abundant, so it is always preferred instead

Question 109

The isotopes uranium-234, uranium-235 and uranium-238 differ from one another mainly in their:

A. Number of protons

B. Atomic number

C. Chemical reactivity

D. Number of neutrons

Question 110

The relative atomic mass of an element is calculated using the masses and abundances of its isotopes through a:

A. Simple addition of isotope masses

B. Weighted average calculation

C. Random estimation

D. Subtraction of isotope masses

Question 111

An element has two isotopes: 75% of its atoms have a mass number of 35, and 25% have a mass number of 37. What is the element's approximate relative atomic mass?

A. 36

B. 35

C. 35.5

D. 37

Question 112

An element has two isotopes: 90% with mass number 10 and 10% with mass number 11. What is its approximate relative atomic mass?

A. 10.1

B. 10.5

C. 10

D. 11

Question 113

An element has two isotopes: 60% with mass number 63 and 40% with mass number 65. What is its approximate relative atomic mass?

A. 64

B. 63.8

C. 63

D. 65

Question 114

Radioactive isotopes used to track the movement or progress of a substance through a biological or industrial system are called:

A. Catalysts

B. Solvents

C. Alloys

D. Tracers

Question 115

In medicine, radioactive isotopes are commonly used for diagnosing diseases by being:

A. Introduced into the body and tracked using imaging equipment

B. Used only to sterilize surgical tools

C. Used only as a food preservative

D. Used only to purify drinking water

Question 116

Certain radioisotopes are used in cancer treatment mainly because they can:

A. Cure all diseases instantly

B. Replace the need for surgery entirely

C. Destroy or shrink cancerous cells with targeted radiation

D. Prevent any cell division in the body

Question 117

Why are radioisotopes useful as tracers in industrial applications, such as detecting leaks in pipelines?

A. They physically block leaks from occurring

B. Their radiation can be detected from outside the pipeline, revealing exactly where a leak occurs

C. They make pipelines invisible to detection

D. They permanently seal any damage in pipelines

Question 118

The technique that uses the decay of carbon-14 to estimate the age of once-living materials is called:

A. Carbon dating

B. Uranium dating

C. Chlorine dating

D. Deuterium dating

Question 119

What is the basic principle behind carbon dating?

A. Carbon-14 amount increases steadily after an organism dies

B. All isotopes of carbon decay at exactly the same rate as carbon-12

C. Carbon dating measures an object's exact mass, not its isotopes

D. Carbon-14 decays at a known, constant rate after an organism dies, so measuring what remains reveals its age

Question 120

A wooden artifact is tested and found to contain much less carbon-14 than a living tree of the same type. What does this suggest about the artifact?

A. It is very young, since it contains almost no carbon at all

B. It was never part of a living organism

C. It is very old, since much of its original carbon-14 has decayed over time

D. Its carbon-14 content increases as it decays

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