CHEM120/ CHEM 120 EXAM 3: INTRODUCTION TO
GENERAL, ORGANIC & BIOLOGICAL CHEMISTRY |
QS & AS| GRADE A| 100% CORRECT (VERIFIED
ANSWERS)- CHAMBERLAIN (NEW 2025/ 2026
UPDATE)
SECTION 1: RADIOACTIVITY & NUCLEAR CHEMISTRY
Question 1
How many half-lives would occur after 30 minutes if a radioactive material has a
half-life of 10 minutes?
A) 1
B) 2
C) 3
D) 4
Correct Answer: C
Rationale: A half-life is the time required for half of a radioactive substance to
decay. Dividing the total elapsed time (30 minutes) by the half-life duration (10
minutes) gives the number of half-lives: 30 ÷ 10 = 3. Each half-life reduces the
remaining amount by 50% .
Question 2
A 60-gram sample of a radioactive material has a half-life of 5 years. How many
grams will remain after 10 years?
A) 30 g
B) 20 g
,C) 15 g
D) 7.5 g
Correct Answer: C
Rationale: Ten years corresponds to two half-lives (10 ÷ 5 = 2). After the first half-
life, 60 g becomes 30 g. After the second half-life, 30 g becomes 15 g. Radioactive
decay follows a predictable exponential pattern .
Question 3
When polonium-225 decays by positron emission, what is the resulting product?
A) Lead-225
B) Bismuth-225
C) Polonium-225
D) Thallium-225
Correct Answer: B
Rationale: Positron emission causes the atomic number to decrease by one while
the mass number remains unchanged. Polonium (atomic number 84) decreases to
Bismuth (atomic number 83), with the same mass number of 225 .
Question 4
What are the effects of alpha decay?
A) Mass number stays the same, atomic number increases by 1
B) Mass number decreases by 4, atomic number decreases by 2
C) Mass number stays the same, atomic number decreases by 1
D) Mass number decreases by 2, atomic number decreases by 4
Correct Answer: B
Rationale: Alpha decay involves the emission of an alpha particle (2 protons and 2
neutrons). This causes the mass number to decrease by 4 and the atomic number
to decrease by 2 .
, Question 5
What are the effects of beta decay?
A) Mass number decreases by 4, atomic number decreases by 2
B) Mass number stays the same, atomic number increases by 1
C) Mass number stays the same, atomic number decreases by 1
D) Mass number decreases by 2, atomic number decreases by 4
Correct Answer: B
Rationale: Beta decay involves the conversion of a neutron to a proton, emitting a
beta particle (electron). The mass number remains unchanged while the atomic
number increases by 1 .
Question 6
Which type of radiation has the lowest penetrating power?
A) Alpha particles
B) Beta particles
C) Gamma rays
D) X-rays
Correct Answer: A
Rationale: Alpha particles consist of two protons and two neutrons, making them
large and heavy. Because of their size, they are easily blocked by paper or skin.
Beta particles have moderate penetration, while gamma rays have very high
penetrating power .
Question 7
Which type of radiation has no mass and no charge?
A) Alpha
B) Beta
GENERAL, ORGANIC & BIOLOGICAL CHEMISTRY |
QS & AS| GRADE A| 100% CORRECT (VERIFIED
ANSWERS)- CHAMBERLAIN (NEW 2025/ 2026
UPDATE)
SECTION 1: RADIOACTIVITY & NUCLEAR CHEMISTRY
Question 1
How many half-lives would occur after 30 minutes if a radioactive material has a
half-life of 10 minutes?
A) 1
B) 2
C) 3
D) 4
Correct Answer: C
Rationale: A half-life is the time required for half of a radioactive substance to
decay. Dividing the total elapsed time (30 minutes) by the half-life duration (10
minutes) gives the number of half-lives: 30 ÷ 10 = 3. Each half-life reduces the
remaining amount by 50% .
Question 2
A 60-gram sample of a radioactive material has a half-life of 5 years. How many
grams will remain after 10 years?
A) 30 g
B) 20 g
,C) 15 g
D) 7.5 g
Correct Answer: C
Rationale: Ten years corresponds to two half-lives (10 ÷ 5 = 2). After the first half-
life, 60 g becomes 30 g. After the second half-life, 30 g becomes 15 g. Radioactive
decay follows a predictable exponential pattern .
Question 3
When polonium-225 decays by positron emission, what is the resulting product?
A) Lead-225
B) Bismuth-225
C) Polonium-225
D) Thallium-225
Correct Answer: B
Rationale: Positron emission causes the atomic number to decrease by one while
the mass number remains unchanged. Polonium (atomic number 84) decreases to
Bismuth (atomic number 83), with the same mass number of 225 .
Question 4
What are the effects of alpha decay?
A) Mass number stays the same, atomic number increases by 1
B) Mass number decreases by 4, atomic number decreases by 2
C) Mass number stays the same, atomic number decreases by 1
D) Mass number decreases by 2, atomic number decreases by 4
Correct Answer: B
Rationale: Alpha decay involves the emission of an alpha particle (2 protons and 2
neutrons). This causes the mass number to decrease by 4 and the atomic number
to decrease by 2 .
, Question 5
What are the effects of beta decay?
A) Mass number decreases by 4, atomic number decreases by 2
B) Mass number stays the same, atomic number increases by 1
C) Mass number stays the same, atomic number decreases by 1
D) Mass number decreases by 2, atomic number decreases by 4
Correct Answer: B
Rationale: Beta decay involves the conversion of a neutron to a proton, emitting a
beta particle (electron). The mass number remains unchanged while the atomic
number increases by 1 .
Question 6
Which type of radiation has the lowest penetrating power?
A) Alpha particles
B) Beta particles
C) Gamma rays
D) X-rays
Correct Answer: A
Rationale: Alpha particles consist of two protons and two neutrons, making them
large and heavy. Because of their size, they are easily blocked by paper or skin.
Beta particles have moderate penetration, while gamma rays have very high
penetrating power .
Question 7
Which type of radiation has no mass and no charge?
A) Alpha
B) Beta
