ATI TEAS 7 Chemistry Basics Exam
(2026 Edition)|| Questions And
Answers With Rationales/Graded
A+/2026 Update/100% Correct
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Section 1: Atomic Structure (Questions 1–15)
1. Which subatomic particle has a positive charge?
A. Electron
B. Neutron
C. Proton
D. Positron
Rationale: Protons are positively charged particles located in the nucleus.
Electrons are negative; neutrons are neutral.
2. The atomic number of an element is determined by the number of:
A. Neutrons
B. Protons
C. Electrons
D. Protons + Neutrons
Rationale: Atomic number = number of protons, unique to each element.
3. Isotopes of an element differ in the number of:
A. Protons
B. Neutrons
C. Electrons
D. Positrons
Rationale: Isotopes have same protons but different neutrons (e.g., Carbon-12 vs
Carbon-14).
,4. What is the mass number of an atom with 8 protons and 10 neutrons?
A. 8
B. 10
C. 18
D. 2
Rationale: Mass number = protons + neutrons = 8 + 10 = 18.
5. Which of the following represents an electron configuration of a noble gas?
A. 1s² 2s¹
B. 1s² 2s² 2p³
C. 1s² 2s² 2p⁶
D. 1s² 2s² 2p⁶ 3s²
Rationale: 1s² 2s² 2p⁶ is neon, a noble gas with full valence shell.
6. An atom that gains an electron becomes a:
A. Cation
B. Anion
C. Isotope
D. Molecule
Rationale: Gain of electron → negative charge → anion.
7. The nucleus of an atom contains:
A. Only protons
B. Protons and neutrons
C. Protons and electrons
D. Neutrons and electrons
Rationale: Nucleus contains protons (positive) and neutrons (neutral). Electrons
orbit outside.
8. How many electrons can the third energy level (n=3) hold?
A. 8
B. 2
C. 18
D. 32
Rationale: Maximum electrons per shell = 2n² = 2(3²) = 18.
, 9. Which of the following has the smallest atomic radius?
A. Na
B. K
C. Cl
D. Rb
Rationale: Across a period, atomic radius decreases. Chlorine is rightmost among
these.
10. Which element has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁴?
A. Oxygen
B. Silicon
C. Sulfur
D. Chlorine
Rationale: Total electrons = 16 → atomic number 16 = sulfur.
11. An atom has 17 protons, 18 neutrons, and 18 electrons. Its charge is:
A. +1
B. –1
C. 0
D. +2
Rationale: Protons = +17, electrons = –18, net charge = –1.
12. Which subatomic particle has negligible mass?
A. Proton
B. Electron
C. Neutron
D. Alpha particle
Rationale: Electron mass is ~1/1836 of a proton.
13. The modern atomic theory states that electrons are found in:
A. Fixed orbits
B. Orbitals (probability clouds)
C. The nucleus
D. Random positions only
Rationale: Quantum model describes electron clouds/orbitals, not fixed planetary
orbits.
(2026 Edition)|| Questions And
Answers With Rationales/Graded
A+/2026 Update/100% Correct
/Instant Download
Section 1: Atomic Structure (Questions 1–15)
1. Which subatomic particle has a positive charge?
A. Electron
B. Neutron
C. Proton
D. Positron
Rationale: Protons are positively charged particles located in the nucleus.
Electrons are negative; neutrons are neutral.
2. The atomic number of an element is determined by the number of:
A. Neutrons
B. Protons
C. Electrons
D. Protons + Neutrons
Rationale: Atomic number = number of protons, unique to each element.
3. Isotopes of an element differ in the number of:
A. Protons
B. Neutrons
C. Electrons
D. Positrons
Rationale: Isotopes have same protons but different neutrons (e.g., Carbon-12 vs
Carbon-14).
,4. What is the mass number of an atom with 8 protons and 10 neutrons?
A. 8
B. 10
C. 18
D. 2
Rationale: Mass number = protons + neutrons = 8 + 10 = 18.
5. Which of the following represents an electron configuration of a noble gas?
A. 1s² 2s¹
B. 1s² 2s² 2p³
C. 1s² 2s² 2p⁶
D. 1s² 2s² 2p⁶ 3s²
Rationale: 1s² 2s² 2p⁶ is neon, a noble gas with full valence shell.
6. An atom that gains an electron becomes a:
A. Cation
B. Anion
C. Isotope
D. Molecule
Rationale: Gain of electron → negative charge → anion.
7. The nucleus of an atom contains:
A. Only protons
B. Protons and neutrons
C. Protons and electrons
D. Neutrons and electrons
Rationale: Nucleus contains protons (positive) and neutrons (neutral). Electrons
orbit outside.
8. How many electrons can the third energy level (n=3) hold?
A. 8
B. 2
C. 18
D. 32
Rationale: Maximum electrons per shell = 2n² = 2(3²) = 18.
, 9. Which of the following has the smallest atomic radius?
A. Na
B. K
C. Cl
D. Rb
Rationale: Across a period, atomic radius decreases. Chlorine is rightmost among
these.
10. Which element has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁴?
A. Oxygen
B. Silicon
C. Sulfur
D. Chlorine
Rationale: Total electrons = 16 → atomic number 16 = sulfur.
11. An atom has 17 protons, 18 neutrons, and 18 electrons. Its charge is:
A. +1
B. –1
C. 0
D. +2
Rationale: Protons = +17, electrons = –18, net charge = –1.
12. Which subatomic particle has negligible mass?
A. Proton
B. Electron
C. Neutron
D. Alpha particle
Rationale: Electron mass is ~1/1836 of a proton.
13. The modern atomic theory states that electrons are found in:
A. Fixed orbits
B. Orbitals (probability clouds)
C. The nucleus
D. Random positions only
Rationale: Quantum model describes electron clouds/orbitals, not fixed planetary
orbits.
