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Atomic Structure Practice Questions

NECO (Nigeria) · NECO Chemistry · 126 free MCQs with instant results and detailed explanations.

126
Total
33
Easy
64
Medium
29
Hard

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Sample Questions from Atomic Structure

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Q1
Easy
Which of the following statements about electrons is true?
A. Electrons have a positive charge.
B. Electrons are heavier than protons.
C. Electrons are found in the nucleus.
D. Electrons have a negative charge.
Show Answer & Explanation
Correct Answer: D
Electrons possess a negative charge, which distinguishes them from protons and neutrons.
Q2
Easy
An atom has 12 protons and 13 neutrons. What is its atomic number?
A. 12
B. 13
C. 25
D. 24
Show Answer & Explanation
Correct Answer: A
The atomic number of an element is defined by the number of protons present in its nucleus, which in this case is 12.
Q3
Easy
How many protons are present in a neutral atom of Carbon-12?
A. 6
B. 12
C. 8
D. 4
Show Answer & Explanation
Correct Answer: A
Carbon-12 has an atomic number of 6, which indicates it has 6 protons in its nucleus.
Q4
Medium
Which of the following statements accurately describes isotopes?
A. Isotopes have the same number of neutrons but different numbers of protons.
B. Isotopes have the same number of protons but different numbers of neutrons.
C. Isotopes are atoms that have different chemical properties.
D. Isotopes are elements that have the same mass.
Show Answer & Explanation
Correct Answer: B
Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons, leading to different mass numbers.
Q5
Medium
An atom of carbon-14 contains 6 protons and 8 neutrons. What is its mass number?
A. 14
B. 6
C. 22
D. 8
Show Answer & Explanation
Correct Answer: A
The mass number of an atom is the sum of its protons and neutrons. For carbon-14, it is 6 protons + 8 neutrons = 14.
Q6
Medium
Which principle explains the arrangement of electrons in an atom?
A. Pauli Exclusion Principle
B. Hund's Rule
C. Aufbau Principle
D. Dalton's Theory
Show Answer & Explanation
Correct Answer: C
The Aufbau Principle states that electrons occupy the lowest energy orbitals first before filling higher energy levels, guiding the arrangement of electrons in an atom.
Q7
Medium
What is the maximum number of electrons that can occupy the p-orbital in a principal energy level?
A. 2
B. 6
C. 8
D. 10
Show Answer & Explanation
Correct Answer: B
Each p-orbital can hold a maximum of 2 electrons, and there are 3 p-orbitals in a principal energy level, resulting in a total of 6 electrons.
Q8
Hard
Which of the following subatomic particles has the least mass?
A. Proton
B. Neutron
C. Electron
D. Positron
Show Answer & Explanation
Correct Answer: C
Electrons have the least mass among subatomic particles, significantly less than protons and neutrons, which are nearly equal in mass.
Q9
Hard
In a neutral atom, if the atomic number is 8, how many electrons are present?
A. 6
B. 8
C. 16
D. 4
Show Answer & Explanation
Correct Answer: B
The atomic number represents the number of protons in a neutral atom, which equals the number of electrons. Therefore, an atomic number of 8 indicates 8 electrons.
Q10
Hard
What is the maximum number of electrons that can occupy the third shell of an atom according to the quantum mechanical model?
A. 8
B. 18
C. 32
D. 2
Show Answer & Explanation
Correct Answer: B
The third shell can hold a maximum of 18 electrons, as calculated using the formula 2nĀ² where n is the shell level (n=3). Thus, 2(3)Ā² = 18.

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Atomic Structure ā€” NECO (Nigeria) NECO Chemistry Practice Questions Online

This page contains 126 practice MCQs for the chapter Atomic Structure in NECO (Nigeria) NECO Chemistry. The questions are organized by difficulty ā€” 33 easy, 64 medium, 29 hard ā€” so you can choose the right level for your preparation.

Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit.