Paper 2 Atomic Structure MCQ Practice
10 multiple-choice questions on atomic structure for IGCSE Chemistry Paper 2. Covers atoms, elements, compounds, subatomic particles, isotopes, and electron arrangement.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Ten multiple-choice questions in the style of IGCSE Chemistry Paper 2. Choose the best answer for each, then check the mark scheme.
Question 1
What is the relative charge of a proton?
A. -1 B. 0 C. +1 D. +2
Answer
C
A proton has a relative charge of +1 and a relative mass of 1. It is found in the nucleus of the atom. Electrons have a charge of -1, and neutrons have no charge (0).
Question 2
An atom of sodium is represented as ²³₁₁Na. How many neutrons does it contain?
A. 11 B. 12 C. 23 D. 34
Answer
B
Neutrons = mass number - atomic number = 23 - 11 = 12. The mass number (23) is the total of protons and neutrons. The atomic number (11) is the number of protons.
Question 3
Which statement about isotopes is correct?
A. Isotopes have different numbers of protons. B. Isotopes have the same mass number but different atomic numbers. C. Isotopes are atoms of the same element with different numbers of neutrons. D. Isotopes always have different chemical properties.
Answer
C
Isotopes are atoms of the same element (same number of protons) with different numbers of neutrons, giving them different mass numbers. They have the same chemical properties because they have the same electron configuration, but different physical properties such as density.
Question 4
What is the electron configuration of a magnesium atom (atomic number 12)?
A. 2, 10 B. 2, 8, 2 C. 2, 4, 6 D. 6, 6
Answer
B
Electrons fill shells in order: the first shell holds a maximum of 2, the second holds 8, and the third holds 8. For 12 electrons: 2 in the first shell, 8 in the second, and 2 in the third, giving 2, 8, 2.
Question 5
Which of the following is a compound?
A. Air B. Copper C. Water D. Bronze
Answer
C
Water (H₂O) is a compound because it contains two different elements (hydrogen and oxygen) chemically bonded together in a fixed ratio. Air is a mixture of gases. Copper is an element. Bronze is an alloy (a mixture of metals).
Question 6
An atom has 17 protons, 18 neutrons, and 17 electrons. What is its mass number?
A. 17 B. 18 C. 34 D. 35
Answer
D
Mass number = protons + neutrons = 17 + 18 = 35. Electrons are not included because their relative mass is negligible (approximately 1/1836 of a proton). This atom is chlorine-35.
Question 7
Which particle is found orbiting the nucleus in energy levels?
A. Proton B. Neutron C. Electron D. Ion
Answer
C
Electrons are found in energy levels (shells) orbiting the nucleus. Protons and neutrons are found inside the nucleus. An ion is a charged atom or group of atoms, not a subatomic particle.
Question 8
Chlorine has two isotopes: ³⁵Cl (75%) and ³⁷Cl (25%). What is the relative atomic mass of chlorine?
A. 35.0 B. 35.5 C. 36.0 D. 37.0
Answer
B
Relative atomic mass = (35 x 75 + 37 x 25) / 100 = (2625 + 925) / 100 = 3550 / 100 = 35.5. The relative atomic mass is the weighted average of the isotopic masses, taking into account their natural abundances.
Question 9
Which statement correctly describes an element?
A. A substance made of two or more types of atom chemically combined. B. A substance that contains only one type of atom. C. A substance that can be separated by physical methods. D. A substance made of molecules only.
Answer
B
An element is a substance that contains only one type of atom. All atoms in an element have the same atomic number (same number of protons). Option A describes a compound, option C describes a mixture, and option D is incorrect because some elements exist as individual atoms (noble gases).
Question 10
A sulfide ion, S²⁻, has the electron configuration 2, 8, 8. How many protons does it have?
A. 14 B. 16 C. 18 D. 20
Answer
B
The sulfide ion has 2 + 8 + 8 = 18 electrons. Since it has a 2- charge, it has gained 2 electrons. Therefore the number of protons = 18 - 2 = 16. Sulfur has atomic number 16. The number of protons never changes when an atom becomes an ion.
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