JUPEB Chemistry
Past Questions
68+ verified Chemistry practice questions for JUPEB. Step-by-step worked answers in 5 Nigerian languages.
Chemistry topics (8)
Sample Chemistry practice questions
1. Number of electrons in O²⁻.
- A. 6
- B. 8
- C. 10
- D. 16
Answer: C
2. Functional group of carboxylic acids.
- A. —OH
- B. —CHO
- C. —COOH
- D. —NH₂
Answer: C
3. The number of moles in 36 g of water (H₂O, M=18) is:
- A. 1
- B. 2
- C. 3
- D. 0.5
Answer: B
4. Which is an alkali?
- A. HCl
- B. NaOH
- C. H₂SO₄
- D. CO₂
Answer: B
5. The bonding in NaCl is:
- A. Covalent
- B. Ionic
- C. Metallic
- D. Hydrogen
Answer: B
6. The most abundant gas in the atmosphere is:
- A. Oxygen
- B. Nitrogen
- C. Carbon dioxide
- D. Argon
Answer: B
7. Isotopes differ in the number of:
- A. Protons
- B. Electrons
- C. Neutrons
- D. Charges
Answer: C
8. The atomic number of an element is the number of:
- A. Neutrons
- B. Protons
- C. Electrons in outer shell
- D. Protons + neutrons
Answer: B
AI Explanation
Atomic number Z = number of protons. It uniquely identifies an element.
9. Which is a covalent compound?
- A. NaCl
- B. MgO
- C. CO₂
- D. KCl
Answer: C
AI Explanation
CO₂ shares electrons between C and O (covalent). NaCl/MgO/KCl are ionic.
10. Avogadro's number is approximately:
- A. 6.022 × 10²³
- B. 6.022 × 10²²
- C. 9.81 × 10²³
- D. 3 × 10⁸
Answer: A
AI Explanation
Avogadro's number = 6.022 × 10²³ entities per mole.
11. What is the empirical formula of hydrogen peroxide (H₂O₂)?
- A. HO
- B. H₂O
- C. H₂O₂
- D. OH₂
Answer: A
AI Explanation
Empirical formula = simplest integer ratio. H₂O₂ simplifies to HO (1:1 ratio).
12. Which is an organic compound?
- A. NaCl
- B. CH₄
- C. H₂O
- D. MgO
Answer: B
AI Explanation
Organic compounds contain carbon (and usually hydrogen). CH₄ (methane) is the simplest organic compound.
13. Which acid is present in vinegar?
- A. Sulphuric acid
- B. Acetic acid
- C. Hydrochloric acid
- D. Nitric acid
Answer: B
AI Explanation
Vinegar contains about 4–8% acetic acid (CH₃COOH).
14. Reduction is the:
- A. Loss of electrons
- B. Gain of electrons
- C. Loss of protons
- D. Gain of mass
Answer: B
AI Explanation
Reduction is gain of electrons (RIG — Reduction Is Gain). Oxidation is loss (OIL).
15. Which element forms the most compounds?
- A. Hydrogen
- B. Carbon
- C. Oxygen
- D. Nitrogen
Answer: B
AI Explanation
Carbon forms millions of compounds due to catenation (bonding to itself) and tetravalency — basis of organic chemistry.
16. What is the chemical formula of water?
- A. H₂O
- B. HO
- C. H₂O₂
- D. OH
Answer: A
AI Explanation
Water = H₂O (two hydrogen atoms covalently bonded to one oxygen).
17. The electron configuration of sodium (atomic number 11) in its ground state is
- A. $1s^2 2s^3 2p^6$
- B. $1s^2 2s^2 2p^7$
- C. $1s^2 2s^2 2p^5 3s^2$
- D. $1s^2 2s^2 2p^6 3s^1$
Answer: D
AI Explanation
Electrons fill in order of increasing energy: 2 in 1s, 2 in 2s, 6 in 2p (the maximum for a p subshell), and the eleventh goes into 3s. A 2p subshell can never hold 7 electrons and an s subshell never holds 3.
18. How many orbitals are there in the third principal energy level (n = 3)?
- A. 9
- B. 18
- C. 6
- D. 3
Answer: A
AI Explanation
The third level has subshells 3s (1 orbital), 3p (3 orbitals) and 3d (5 orbitals), a total of $n^2 = 9$ orbitals. Since each orbital holds 2 electrons, the level holds a maximum of 18 electrons, which is the tempting wrong answer.
19. An element has the electron configuration $1s^2 2s^2 2p^6 3s^2 3p^5$. In which group of the Periodic Table is it found?
- A. Group 18
- B. Group 2
- C. Group 17
- D. Group 15
Answer: C
AI Explanation
The outer shell has $3s^2 3p^5$, that is 7 valence electrons, which places the element in Group 17 (the halogens); it is chlorine. Group 18 elements have a full $p^6$ outer shell.
20. Isotopes of the same element differ in their
- A. number of neutrons.
- B. number of electrons.
- C. number of protons.
- D. chemical properties.
Answer: A
AI Explanation
Isotopes have the same atomic number (protons and, in the neutral atom, electrons) but different mass numbers because of different numbers of neutrons. Their chemical properties are essentially identical since these depend on electron arrangement.
21. Across a period from left to right in the Periodic Table, the atomic radius generally
- A. stays constant because the number of shells is the same.
- B. decreases because nuclear charge increases while shielding stays roughly constant.
- C. increases because electronegativity increases.
- D. increases because more electrons are added.
Answer: B
AI Explanation
Electrons are added to the same shell while protons are added to the nucleus, so the increasing nuclear charge pulls the outer electrons closer and the radius shrinks. The same number of shells does not mean the same size.
22. Chlorine consists of 75% of the isotope $^{35}\text{Cl}$ and 25% of $^{37}\text{Cl}$. Calculate its relative atomic mass.
- A. 35.0
- B. 36.5
- C. 35.5
- D. 36.0
Answer: C
AI Explanation
Relative atomic mass $= \dfrac{(75 \times 35) + (25 \times 37)}{100} = \dfrac{2625 + 925}{100} = 35.5$. Taking a simple average of 35 and 37 gives 36, which ignores the abundances.
23. An atom of chlorine is represented as $^{35}_{17}\text{Cl}$. How many neutrons does it contain?
- A. 35
- B. 18
- C. 17
- D. 52
Answer: B
AI Explanation
Neutrons = mass number − atomic number = 35 − 17 = 18. The value 17 is the number of protons (and electrons), and 52 comes from adding the two numbers.
24. Which of the following elements has the highest first ionisation energy?
- A. aluminium
- B. magnesium
- C. sodium
- D. silicon
Answer: D
AI Explanation
Ionisation energy generally rises across a period as nuclear charge increases: Na 496, Mg 738, Al 578, Si 786 kJ mol$^{-1}$. Aluminium is lower than magnesium because its outer electron is in the higher-energy 3p subshell, but silicon, further right, exceeds them all.
25. The maximum number of electrons that can occupy a d subshell is
- A. 14
- B. 6
- C. 2
- D. 10
Answer: D
AI Explanation
A d subshell has five orbitals, each holding two electrons, giving 10. The values 2, 6 and 14 are the capacities of s, p and f subshells respectively.
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