Chemistry WAEC 2025 Past Questions (Objective & Theory)
Attempt this paper under exam conditions, then mark yourself using the answers.
Section A — Objective
Question 1
The number of protons in an atom is called its
A. Atomic number
B. Mass number
C. Valency
D. Isotope number
Answer: A. Atomic number = number of protons. Mass number = protons + neutrons.
Question 2
An atom with electronic configuration 2, 8, 1 is most likely to form an ion with charge
A. +1
B. -1
C. +3
D. -3
Answer: A. One outer electron is lost to form a +1 ion (e.g. sodium, Na⁺).
Question 3
The bond formed by the transfer of electrons is called
A. Ionic bond
B. Covalent bond
C. Metallic bond
D. Hydrogen bond
Answer: A. Ionic bonds involve electron transfer; covalent bonds involve sharing.
Question 4
Which of the following is an alkali?
A. Hydrochloric acid
B. Distilled water
C. Sodium hydroxide solution
D. Carbon dioxide
Answer: C. Sodium hydroxide is a soluble base (an alkali). Hydrochloric acid is an acid; water is neutral.
Question 5
How many moles are in 11 g of carbon dioxide (CO₂)? (C = 12, O = 16)
A. 0.25 mol
B. 0.5 mol
C. 2 mol
D. 4 mol
Answer: A. Mᵣ of CO₂ = 12 + 32 = 44. Moles = 11 ÷ 44 = 0.25 mol.
Question 6
The general formula of alkenes is
A. CₙH₂ₙ₊₂
B. CₙH₂ₙ
C. CₙH₂ₙ₋₂
D. CₙHₙ
Answer: B. Alkenes have the general formula CₙH₂ₙ (e.g. ethene C₂H₄).
Section B — Theory
Question 1 — Theory
State two differences between ionic and covalent compounds.
Model answer (any two):
1. Ionic compounds have high melting points; covalent compounds have low melting points. 2. Ionic compounds conduct electricity when molten or in solution; covalent compounds do not. 3. Ionic bonds involve electron transfer; covalent bonds involve electron sharing.
Question 2 — Theory
Write the electronic configuration of oxygen (atomic number 8).
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