Top IJMB Chemistry Questions with Answers.

Welcome to today’s Chemistry tutorial on AllCBTs!
This session covers some high-probability IJMB Chemistry past questions. These are commonly asked concepts in organic chemistry, chemical reactions, stoichiometry, and oxidation states. If you’re preparing for IJMB, JUPEB, WAEC, or NECO, this guide is a must-read!

Grab your writing materials and calculators — let’s dive in.

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You can watch the full class in the video below:

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Question 1: Elements with Variable Oxidation States

Question:
Which of the following elements exhibits variable oxidation states and forms colored compounds?

Options:
A. Sodium
B. Calcium
C. Iron
D. Argon

Correct Answer: C. Iron

Explanation:
Transition elements like iron (Fe) show variable oxidation states (Fe²⁺, Fe³⁺) and form colored compounds. Sodium and calcium are not transition elements, and argon is a noble gas with no chemical reactivity.

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Question 2: Neutralization Reaction Calculation

Question:
What volume of 0.5 M NaOH is required to neutralize 25 cm³ of 0.1 M HCl?

Step-by-step:

• Reaction: HCl + NaOH→NaCl + H₂O\text{HCl + NaOH} \rightarrow \text{NaCl + H₂O}HCl + NaOH→NaCl + H₂O
• Use the formula: CAVA=CBVB⇒VB=CA×VACBC_A V_A = C_B V_B \Rightarrow V_B = \frac{C_A \times V_A}{C_B}CA​VA​=CB​VB​⇒VB​=CB​CA​×VA​​
• Substitute: VB=0.1×250.5=2.50.5=5.0 cm³V_B = \frac{0.1 \times 25}{0.5} = \frac{2.5}{0.5} = 5.0 \text{ cm³}VB​=0.50.1×25​=0.52.5​=5.0 cm³

Correct Answer: 5.0 cm³

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Question 3: Temperature and Reaction Rate

Question:
Why does the rate of chemical reaction increase with temperature?

Options:
A. Activation energy increases
B. More reactants are formed
C. Molecular collisions are reduced
D. Molecules have energy greater than activation energy

Correct Answer: D. Molecules have energy greater than the activation energy

Explanation:
As temperature increases, particles move faster, and more of them attain the required activation energy, increasing the rate of reaction.

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Question 4: Highest Energy Orbital

Question:
Which of the following orbitals has the highest energy?

Options:
A. 3d
B. 4s
C. 4p
D. 4d

Correct Answer: C. 4p

Explanation:
Energy levels increase in this order:
4s < 3d < 4p < 4d. Therefore, 4p has the highest energy among the listed.

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Question 5: Polymerization Compound

Question:
Which compound undergoes addition polymerization?

Options:
A. Ethyne
B. Ethanol
C. Acetic acid
D. Glucose

Correct Answer: A. Ethyne

Explanation:
Addition polymerization is characteristic of unsaturated hydrocarbons (alkenes, alkynes). Ethyne (C₂H₂) undergoes polymerization to form polyethyne.

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Question 6: Molecular Formula from Empirical Formula

Question:
A compound has an empirical formula CH and molecular mass of 78. Find its molecular formula.

Steps:

1. Empirical formula mass of CH = 12 + 1 = 13
2. Molecular formula mass = 78
3. Number of units = 78 / 13 = 6
4. Molecular formula = C₆H₆

Correct Answer: C₆H₆ (Benzene)

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Question 7: Oxidation Number of Nitrogen in HNO₃

To find the oxidation number of nitrogen:

Let N = x
Oxygen = -2 × 3 = -6
Hydrogen = +1 +1+x−6=0⇒x=+5+1 + x – 6 = 0 \Rightarrow x = +5+1+x−6=0⇒x=+5

Correct Answer: +5

Watch more educational videos and past questions: https://youtube.com/@allcbts

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Final Tips for IJMB & JUPEB Chemistry Exams

• Understand concepts, not just formulas. Most questions test application, not memorization.
• Practice writing balanced chemical equations, especially for acid-base and redox reactions.
• Master topics like oxidation numbers, hybridization, polymerization, and empirical/molecular formula conversions.
• Solve past questions within time limits to improve speed and confidence.

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