What this area covers
- Atomic structure and the periodic table
- Ionic, covalent and hydrogen bonds
- States of matter and phase changes
- Chemical reactions and balancing equations
- Solutions, concentration and solubility
- Acids, bases and the pH scale
Concepts that come up most in our question bank:
Where students lose marks
Bond type questions turn on whether electrons are shared or transferred. Hydrogen bonds are also routinely miscounted as true chemical bonds when they are intermolecular attractions.
How to study it
Anchor bonding to the metal / nonmetal rule: metal plus nonmetal transfers electrons and is ionic, nonmetal plus nonmetal shares them and is covalent. For pH, remember the scale is logarithmic — each whole number is a tenfold change, which is often what the question is really testing.
Practice questions
Answer these, then check them to see the full explanation for every option — including why each wrong answer is wrong.
- Question 1
How many valence electrons does an atom of oxygen (atomic number 8) have?
Correct answer: B. Oxygen has 8 electrons total. Electron configuration: 2 electrons in the first shell, 6 in the second shell. Valence electrons are in the outermost shell, so oxygen has 6 valence electrons. This is consistent with its position in Group 16 (VIA) of the periodic table.
- A. 2 is the number of electrons in oxygen's first (inner) shell, not the valence shell.
- C. 8 is the total number of electrons (and protons), not the number of valence electrons.
- D. 4 is the number of valence electrons for carbon (Group 14), not oxygen (Group 16).
- Question 2
In a chemical equation, what does the arrow (→) represent?
Correct answer: B. The single arrow (→) in a chemical equation means 'yields' or 'produces.' Reactants are on the left side, products on the right. Example: 2H₂ + O₂ → 2H₂O means hydrogen and oxygen react to produce water.
- A. An equals sign (=) indicates equality. The arrow shows the direction of the reaction, not equality.
- C. A reversible reaction is indicated by a double arrow (⇌), not a single arrow.
- D. Energy absorption is indicated by adding 'energy' or 'heat' to the reactant side, not by the arrow itself.
- Question 3
Which of the following is a property of acids?
Correct answer: B. Acids have a sour taste (like lemons and vinegar), a pH below 7, turn blue litmus paper red, and produce hydrogen ions (H⁺) when dissolved in water. Common acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and citric acid.
- A. Bitter taste and slippery feel are properties of bases, not acids.
- C. Acids turn blue litmus paper red. Bases turn red litmus paper blue.
- D. Producing hydroxide ions (OH⁻) is a property of bases (e.g., NaOH → Na⁺ + OH⁻). Acids produce hydrogen ions (H⁺).
- Question 4
What type of reaction occurs when an acid and a base react to form water and a salt?
Correct answer: B. A neutralization reaction occurs when an acid reacts with a base to produce water and a salt. Example: HCl + NaOH → NaCl + H₂O. The H⁺ from the acid combines with the OH⁻ from the base to form water, and the remaining ions form the salt.
- A. Combustion involves a substance reacting with oxygen, producing heat and light (e.g., burning fuel).
- C. Decomposition involves a single compound breaking down into two or more simpler substances (e.g., 2H₂O → 2H₂ + O₂).
- D. Single replacement involves one element replacing another in a compound (e.g., Zn + CuSO₄ → ZnSO₄ + Cu).
- Question 5
What is the chemical formula for table salt?
Correct answer: B. Table salt is sodium chloride (NaCl), an ionic compound formed when sodium (Na⁺) transfers an electron to chlorine (Cl⁻). It is the most common salt and is essential for human physiology.
- A. NaOH is sodium hydroxide (lye), a strong base, not table salt.
- C. KCl is potassium chloride, a salt substitute sometimes used by people on sodium-restricted diets.
- D. CaCO₃ is calcium carbonate (limestone, chalk, antacid tablets), not table salt.
- Question 6
Which of the following correctly describes an isotope?
Correct answer: B. Isotopes are atoms of the same element (same number of protons/atomic number) that have different numbers of neutrons, giving them different mass numbers. For example, carbon-12 (6 protons, 6 neutrons) and carbon-14 (6 protons, 8 neutrons) are isotopes of carbon.
- A. Changing the number of protons changes the element entirely. Isotopes have the same number of protons.
- C. Atoms of different elements with the same neutron count are not isotopes — isotopes must be the same element.
- D. Atoms with the same mass number but different atomic numbers are called isobars, not isotopes.
- Question 7
Which state of matter has a definite volume but no definite shape?
Correct answer: B. Liquids have a definite volume (they occupy a fixed amount of space) but no definite shape (they take the shape of their container). Particles in a liquid are close together but can slide past each other.
- A. Solids have both a definite volume and a definite shape. Particles are tightly packed in fixed positions.
- C. Gases have neither a definite volume nor a definite shape. They expand to fill their container.
- D. Plasma is an ionized gas with no definite shape or volume, found in stars and lightning.
- Question 8
What does the law of conservation of mass state?
Correct answer: B. The law of conservation of mass states that in a chemical reaction, the total mass of the reactants equals the total mass of the products. Atoms are rearranged during reactions but are not created or destroyed. This is why chemical equations must be balanced.
- A. Mass cannot be created in a chemical reaction. The total mass remains constant.
- C. Products have the same total mass as reactants — neither more nor less.
- D. While Einstein's E=mc² relates energy and mass, this is not what the law of conservation of mass states in the context of chemical reactions.
- Question 9
Which of the following elements is a noble gas?
Correct answer: B. Neon is a noble gas (Group 18/VIIIA). Noble gases have a full outer electron shell, making them extremely stable and largely unreactive. Other noble gases include helium, argon, krypton, xenon, and radon.
- A. Sodium is an alkali metal (Group 1/IA), highly reactive and easily loses one electron.
- C. Nitrogen is a nonmetal in Group 15/VA. It forms covalent bonds and is a major component of the atmosphere.
- D. Nickel is a transition metal used in alloys and coins.
- Question 10
What happens to molecules when a substance changes from a liquid to a gas (evaporation)?
Correct answer: B. During evaporation, molecules absorb energy (heat), increasing their kinetic energy. This allows them to overcome intermolecular forces and escape the liquid phase, spreading farther apart as gas molecules. Phase changes are physical changes — the molecules themselves are not altered.
- A. Slowing down and moving closer together describes condensation or freezing, not evaporation.
- C. Molecules are not destroyed during phase changes. Their chemical identity remains the same; only their arrangement and energy change.
- D. Molecules in a gas have more kinetic energy than in a liquid, not less.
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