WGU D425 INTRODUCTION TO CHEMISTRY PREP EXAM 2026 ALL QUESTIONS AND CORRECT DETAILED ANSWERS WITH RATIONALES ALREADY A GRADED WITH EXPERT FEEDBACK |NEW AND REVISED

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WGU D425 INTRODUCTION TO
CHEMISTRY PREP EXAM 2026 ALL
QUESTIONS AND CORRECT DETAILED
ANSWERS WITH RATIONALES ALREADY A
GRADED WITH EXPERT FEEDBACK |NEW
AND REVISED

1. How is matter classified?
 A) Elements and compounds only
 B) Pure substances and mixtures
 C) Solids, liquids, and gases only
 D) Atoms and molecules only
Rationale: Matter is classified into two main categories: pure
substances (elements and compounds with fixed composition)
and mixtures (physical combinations of two or more substances
that retain their individual identities).
2. What is the charge of an electron?
 A) +1
 B) -1
 C) 0 (neutral)

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 D) +2
Rationale: An electron carries a fundamental unit of negative
electrical charge (-1). Protons have a +1 charge, and neutrons
are neutral (0 charge).
3. An atom has 17 protons, 18 neutrons, and 17 electrons. What is
the mass number of this atom?
 A) 17
 B) 18
 C) 35
 D) 34
Rationale: Mass number = protons + neutrons = 17 + 18 = 35.
Electrons do not contribute to mass number because their mass
is negligible.
4. What is the atomic number of an atom with 15 protons?
 A) 15
 B) 16
 C) 30
 D) 31
Rationale: The atomic number (Z) is defined as the number of
protons in the nucleus. Since the atom has 15 protons, its atomic
number is 15.
5. Which of the following best describes an isotope?
 A) Atoms with the same number of neutrons but different protons
 B) Atoms with the same number of protons but different
numbers of neutrons
 C) Atoms with the same mass number but different atomic
numbers

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 D) Atoms with different numbers of electrons only
Rationale: Isotopes of an element have identical proton counts
(same element) but vary in neutron number, leading to different
mass numbers.
6. Which subatomic particle has a negative charge and is found in
orbitals around the nucleus?
 A) Proton
 B) Neutron
 C) Electron
 D) Positron
Rationale: Electrons are negatively charged particles that occupy
electron clouds or orbitals surrounding the nucleus; protons are
positive, neutrons neutral.
7. What is the mass number of an atom?
 A) Number of protons
 B) Number of neutrons
 C) Number of protons + number of neutrons
 D) Number of electrons + number of protons
Rationale: The mass number is the sum of protons and neutrons
in an atom's nucleus. Electrons have negligible mass.
8. When an electron moves from a higher energy level to a lower
energy level:
 A) Energy is absorbed
 B) Energy is released
 C) No energy change occurs

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 D) The electron is destroyed
Rationale: When an electron transitions from a higher to a lower
energy level, energy is released, often in the form of light (photon
emission).
9. Which of the following elements is a noble gas?
 A) Oxygen
 B) Chlorine
 C) Neon
 D) Sodium
Rationale: Noble gases are found in Group 18 of the periodic
table and include helium, neon, argon, krypton, xenon, and
radon. Neon is a noble gas with a full valence electron shell.
10. What is the correct electron configuration for oxygen (atomic
number 8)?
 A) 1s²2s²2p³
 B) 1s²2s²2p⁴
 C) 1s²2s²2p⁵
 D) 1s²2s²2p⁶
Rationale: Oxygen has 8 electrons. The electron configuration is
1s²2s²2p⁴, with the 2p subshell containing 4 electrons. The
configuration 1s²2s²2p⁶ would represent neon.
11. Which of the following periodic trends decreases as you move
from left to right across a period?
 A) Atomic radius
 B) Ionization energy
 C) Electronegativity