200+ QUESTIONS & ANSWERS WITH
RATIONALES
,WGU D425 Intro to Chemistry — Questions
Question 1
Which subatomic particle determines the identity of an element?
A. Electron
B. Neutron
C. Proton
D. Photon
Answer: C. Proton
Rationale: The number of protons in an atom is its atomic number, which uniquely identifies
the element. Changing the number of electrons produces an ion, while changing neutrons
produces an isotope.
Question 2
An atom contains 12 protons, 12 neutrons, and 10 electrons. What is its overall charge?
A. 0
B. +1
C. +2
D. −2
Answer: C. +2
Rationale: Protons contribute +12 and electrons contribute −10. Therefore, the net charge is
+12 − 10 = +2.
Question 3
What is the mass number of an atom containing 15 protons and 16 neutrons?
,A. 15
B. 16
C. 30
D. 31
Answer: D. 31
Rationale: Mass number equals the total number of protons and neutrons:
15 + 16 = 31.
Electrons are not included in the mass number.
Question 4
Which statement correctly describes isotopes?
A. They have different numbers of protons but the same neutrons.
B. They have the same number of protons but different numbers of neutrons.
C. They have the same number of electrons but different atomic numbers.
D. They always have different chemical symbols.
Answer: B. They have the same number of protons but different numbers of neutrons.
Rationale: Isotopes are atoms of the same element, so they must have the same number of
protons. Their neutron numbers differ, producing different mass numbers.
Question 5
Which element has the electron configuration 1s² 2s² 2p⁶ 3s¹?
A. Magnesium
B. Sodium
, C. Aluminum
D. Neon
Answer: B. Sodium
Rationale: The configuration contains 11 electrons. An atom with 11 electrons is sodium (Na).
Its outermost electron occupies the 3s orbital.
Question 6
Which element is the most electronegative?
A. Fluorine
B. Oxygen
C. Chlorine
D. Nitrogen
Answer: A. Fluorine
Rationale: Fluorine has the highest electronegativity of all elements. Electronegativity
generally increases from left to right across a period and upward within a group.
Question 7
Which trend generally occurs as atomic radius increases down a group?
A. The number of occupied electron shells decreases.
B. Nuclear charge becomes zero.
C. Additional electron shells are added.
D. Electronegativity always increases.
Answer: C. Additional electron shells are added.
RATIONALES
,WGU D425 Intro to Chemistry — Questions
Question 1
Which subatomic particle determines the identity of an element?
A. Electron
B. Neutron
C. Proton
D. Photon
Answer: C. Proton
Rationale: The number of protons in an atom is its atomic number, which uniquely identifies
the element. Changing the number of electrons produces an ion, while changing neutrons
produces an isotope.
Question 2
An atom contains 12 protons, 12 neutrons, and 10 electrons. What is its overall charge?
A. 0
B. +1
C. +2
D. −2
Answer: C. +2
Rationale: Protons contribute +12 and electrons contribute −10. Therefore, the net charge is
+12 − 10 = +2.
Question 3
What is the mass number of an atom containing 15 protons and 16 neutrons?
,A. 15
B. 16
C. 30
D. 31
Answer: D. 31
Rationale: Mass number equals the total number of protons and neutrons:
15 + 16 = 31.
Electrons are not included in the mass number.
Question 4
Which statement correctly describes isotopes?
A. They have different numbers of protons but the same neutrons.
B. They have the same number of protons but different numbers of neutrons.
C. They have the same number of electrons but different atomic numbers.
D. They always have different chemical symbols.
Answer: B. They have the same number of protons but different numbers of neutrons.
Rationale: Isotopes are atoms of the same element, so they must have the same number of
protons. Their neutron numbers differ, producing different mass numbers.
Question 5
Which element has the electron configuration 1s² 2s² 2p⁶ 3s¹?
A. Magnesium
B. Sodium
, C. Aluminum
D. Neon
Answer: B. Sodium
Rationale: The configuration contains 11 electrons. An atom with 11 electrons is sodium (Na).
Its outermost electron occupies the 3s orbital.
Question 6
Which element is the most electronegative?
A. Fluorine
B. Oxygen
C. Chlorine
D. Nitrogen
Answer: A. Fluorine
Rationale: Fluorine has the highest electronegativity of all elements. Electronegativity
generally increases from left to right across a period and upward within a group.
Question 7
Which trend generally occurs as atomic radius increases down a group?
A. The number of occupied electron shells decreases.
B. Nuclear charge becomes zero.
C. Additional electron shells are added.
D. Electronegativity always increases.
Answer: C. Additional electron shells are added.
