WAEC (WASSCE) Chemistry Past Questions and Answers (2026)

Answer: C

The elements are represented by their atomic numbers: Q (20), R (16), S (10), and T (8). Element T, with an atomic number of 8, corresponds to oxygen, which is typically reactive. Element S, with an atomic number of 10, corresponds to neon, a noble gas, which is unreactive due to its full valence shell. Element R (16) corresponds to sulfur, which is reactive, and element Q (20) corresponds to calcium, which is also reactive. Therefore, the correct answer is D, as T is not unreactive but S is. However, since the question asks for unreactive elements, the correct answer should actually be C, S, not D, T.

Answer: D

Chlorine has seven electrons in its outer shell and needs one more to achieve a stable octet configuration. By gaining one electron, it becomes Cl⁻, which has a full outer shell. Option A is incorrect because losing one electron would result in Cl⁺, not Cl⁻. Option B is incorrect because sharing an electron typically occurs in covalent bonding, not in the formation of an anion. Option C is incorrect because donating a lone pair of electrons does not lead to the formation of Cl⁻; it involves sharing rather than gaining electrons.

Answer: C

The combining power of an element indicates how many atoms of the element can combine with atoms of other elements. Element Z has a combining power of 3, meaning it can form compounds where it combines with three atoms of another element or can combine with one atom of an element that has a combining power of 3. In option C (Z₂O₃), Z combines with three oxygen atoms, which is consistent with its combining power of 3. Option A (ZSO₃) suggests Z combines with one sulfur and three oxygen atoms, which does not match the combining power of 3. Option B (Z₃Cl₂) implies Z combines with two chlorine atoms, which does not utilize its full combining power. Option D (ZS₃) suggests Z combines with three sulfur atoms, which is also inconsistent with the combining power of 3 since it would require Z to have a combining power of 1. Therefore, C is the only correct formula that reflects the combining power of Z accurately.

Answer: C

Electrovalent compounds, also known as ionic compounds, are formed by the electrostatic attraction between positively and negatively charged ions. They typically have high melting points due to the strong ionic bonds that require a significant amount of energy to break. Option A is incorrect because electrovalent compounds are generally not soluble in ethanol; they are more soluble in polar solvents like water. Option B is misleading as electrovalent compounds can have varying molar masses, and high molar mass is not a defining characteristic. Option D is incorrect because while some electrovalent compounds can act as oxidizing agents, this is not a general characteristic of all such compounds.

Answer: A

Potassium (K) is a metal that readily loses one electron to form a positively charged ion (K+), while oxygen (O) is a non-metal that gains two electrons to form a negatively charged ion (O2-). The electrostatic attraction between the oppositely charged ions (K+ and O2-) results in an ionic bond. The other options are incorrect because: B. Metallic bonds occur between metal atoms, which is not the case here; C. Covalent bonds involve the sharing of electrons between non-metals, which does not apply to K and O; D. Dative bonds involve one atom providing both electrons for a bond, which is not relevant in this ionic compound.

Answer: C

A co-ordinate covalent bond is formed when one atom donates both electrons to a bond. In the case of NH₄ (ammonium ion), the nitrogen atom donates a pair of electrons to bond with a proton (H⁺), forming a co-ordinate covalent bond. HCl (hydrochloric acid) has a polar covalent bond, CH₄ (methane) has non-polar covalent bonds, and NaCl (sodium chloride) consists of ionic bonds, none of which involve co-ordinate covalent bonding.

Answer: C

The electrostatic force of attraction between ions is determined by Coulomb's law, which states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between the charges. In this case, sodium ion (Na+) has a +1 charge and halide ions (F-, Br-, Cl-, I-) have a -1 charge. The size of the halide ions increases from F- to I-, which increases the distance between the ions and decreases the force of attraction. Therefore, NaF has the smallest halide ion (F-) and the greatest electrostatic attraction. NaCl has a larger ion than NaF but smaller than NaBr and NaI, leading to a weaker attraction than NaF. NaBr has an even larger ion than NaCl, resulting in a weaker attraction than NaCl. NaI has the largest ion, resulting in the weakest attraction. Thus, the correct answer is C. NaF.

Answer: B

Chlorine (B) is a highly reactive non-metal that readily forms ionic compounds with metals by accepting electrons, making it more reactive than nitrogen, sulphur, or carbon. Nitrogen (A) is relatively inert under standard conditions, sulphur (C) reacts less readily with metals compared to chlorine, and carbon (D) typically forms covalent bonds rather than ionic ones with metals.

Answer: D

The correct answer is D, as lead is a dense material that effectively blocks radiation, making it suitable for storing radioactive materials. Option A is incorrect because paraffin oil does not provide adequate shielding from radiation. Option B is incorrect because ultraviolet light does not protect against radioactive decay or radiation. Option C is also incorrect, as a cool, dark cupboard does not offer any protective shielding from radiation.

Answer: A

In the given equation, 234_90Th (Thorium-234) undergoes beta decay, which means it emits a beta particle (β-) and transforms into a new element. The atomic number decreases by 1 (from 90 to 89), while the mass number remains the same (234). This results in the formation of 234_89Pa (Protactinium-234). Therefore, x = 89 and y = 234, making option A (91 234) incorrect. Option B (92 235) is incorrect as it suggests an increase in atomic number and mass. Option C (89 235) is incorrect because the mass number should remain 234. Option D (88 238) is incorrect as it suggests a decrease in atomic number and an increase in mass number, which does not correspond to beta decay.

Answer: B

CCl₄, or carbon tetrachloride, has a central carbon atom bonded to four chlorine atoms. The molecular geometry is determined by the arrangement of these bonds around the central atom. Due to the four equivalent C-Cl bonds and the absence of lone pairs on the carbon atom, the molecule adopts a tetrahedral shape to minimize electron pair repulsion, as described by VSEPR theory. Option A (Pyramidal) is incorrect because pyramidal shapes have lone pairs that create a distortion, which is not the case here. Option C (Trigonal planar) is incorrect because it applies to molecules with three bonded atoms and no lone pairs. Option D (Linear) is incorrect as it describes a molecule with two bonded atoms and no lone pairs, which does not apply to CCl₄.

Answer: B

As boiling water changes to steam, the molecules gain energy and move further apart, which increases the degree of disorder or entropy in the system. Option A is incorrect because the temperature remains constant during the phase change (at boiling point). Option C is incorrect because the number of molecules remains the same; they are simply changing from liquid to gas. Option D is incorrect because activation energy refers to the energy needed to initiate a reaction, not relevant in this phase change context.