JAMB Chemistry 2021 past questions

Checked by the Skolra question team · Last updated 23 October 2026

Ten questions from the 2021 JAMB Chemistry paper, with answers and explanations. We hold 40 questions from this paper, and the Skolra app has all of them.

JAMB Chemistry 2021 questions and answers

1.
A chemical process in which there is a gain of electrons is known as?
1. A
  Reduction
  Correct
2. B
  Oxidation
3. C
  Neutralization
4. D
  Hydrolysis
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Answer: A
Reduction is the chemical process in which a species gains electrons.
A simple way to remember this is the mnemonic OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). So any process where electrons are gained by a substance is a reduction process, and the substance that gains the electrons is called the oxidizing agent (it gets reduced).
Oxidation is the exact opposite — it is the loss of electrons, not the gain, so a candidate who mixes up the two directions of electron transfer would wrongly pick this.
2.
The inherited traits of an organism are controlled by?
1. A
  Genes
  Correct
2. B
  Enzymes
3. C
  Chromosomes
4. D
  Hormones
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Answer: A
Genes are correct. Genes are the units of heredity — segments of DNA that carry the instructions for an organism's traits (such as eye colour, blood group, or seed shape) and are passed from parents to offspring.
Chromosomes are tempting because they are the thread-like structures found in the nucleus that carry the genes, but it is the genes on them, not the chromosomes themselves, that determine specific traits — a candidate who confuses the carrier with the unit of information picks this by mistake.
Hormones are chemical messengers that regulate body activities like growth and metabolism; they do not carry hereditary information.
3.
The maximum electron in N shell is?
1. A
  18
2. B
  32
  Correct
3. C
  8
4. D
  16
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Answer: B
The maximum number of electrons any shell can hold is found using the formula 2n², where n is the shell number.
The shells are labelled K, L, M, N, corresponding to n = 1, 2, 3, 4 respectively. The N shell is the fourth shell, so n = 4.
Maximum electrons = 2n² = 2 × 4² = 2 × 16 = 32.
The value 18 is the maximum for the M shell (n = 3), where 2 × 3² = 18, so a candidate who mixes up the shell number gets this instead. The value 8 is the maximum for the L shell (n = 2), since 2 × 2² = 8. The value 16 comes from squaring n = 4 correctly but forgetting to multiply by 2, giving an incomplete calculation.
4.
The only metal that is anti-bacterial is?
1. A
  Zinc
2. B
  Silver
  Correct
3. C
  Iron
4. D
  Copper
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Answer: B
Silver is the metal well known for its anti-bacterial (oligodynamic) property. Silver ions are able to disrupt the cell membrane and enzyme systems of bacteria, which is why silver has long been used in wound dressings, water storage vessels, and coatings for medical instruments to prevent bacterial growth.
Copper is a tempting choice because it also shows some antimicrobial action, but it is not the metal traditionally singled out for this property in the chemistry syllabus — silver is the standard answer.
5.
The fourteen elements (atomic number 90-103) after actinium are called?
1. A
  Lanthanides
2. B
  Actinides
  Correct
3. C
  Noble gases
4. D
  Transition elements
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Answer: B
The elements with atomic numbers 90 to 103 come immediately after actinium (atomic number 89) in the periodic table. This set of fourteen elements is called the actinides (also written actinoids).
The actinides belong to the f-block of the periodic table and include familiar elements such as thorium, uranium, and plutonium. They are placed in a separate row below the main body of the table, along with the lanthanides, to keep the table compact.
6.
What is the IUPAC name for the following compound? HC $\equiv$ CCH $_{3}$
1. A
  Prop-2-yne
2. B
  Propan-1-yne
3. C
  Propa-1,2-diene
4. D
  Prop-1-yne
  Correct
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Answer: D
The compound is HC≡C–CH₃, a three-carbon chain with a triple bond and one methyl group.
Step 1: The parent chain has 3 carbons, so the base name is "prop-". Since there is a carbon-carbon triple bond, the suffix is "-yne", giving "propyne".
Step 2: To number the chain, count from the end nearest the triple bond so it gets the lowest possible locant. Counting from the H≡C end: C1≡C2–C3(H₃). The triple bond sits between carbon 1 and carbon 2, so the locant is 1.
Correct answer: prop-1-yne (the everyday name "propyne" refers to the same compound).
7.
In troposphere, the two types of pollutants are?
1. A
  Gaseous and particulate pollutants
2. B
  Organic and inorganic pollutants
3. C
  Natural and artificial pollutants
4. D
  Primary and secondary pollutants
  Correct
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Answer: D
Pollutants found in the troposphere are grouped into primary pollutants and secondary pollutants, based on how they get into the air.
Primary pollutants are released directly from a source into the atmosphere, for example carbon(II) oxide and soot from vehicle exhausts, sulphur(IV) oxide from burning fossil fuels, and oxides of nitrogen from combustion.
Secondary pollutants are not emitted directly; they form afterwards when primary pollutants react with each other or with other substances already in the air, for example ozone and the acidic compounds that cause acid rain.
8.
Give the common name for the following compound (CH $_{3}$ ) $_{2}$ CH CH $_{2}$ -Br
1. A
  sec-Butyl bromide
2. B
  Isobutyl bromide
  Correct
3. C
  n-Butyl bromide
4. D
  tert-Butyl bromide
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Answer: B
The compound given is (CH3)2CH-CH2-Br. The bromine sits on a CH2 group, and that CH2 is joined to a carbon that already carries two methyl groups.
This arrangement is exactly what chemists call isobutyl bromide (systematically, 1-bromo-2-methylpropane). That is the correct common name.
Candidates often confuse the butyl bromide isomers because they all share the formula C4H9Br.
9.
The gas which causes global warming is?
1. A
  Oxygen
2. B
  Nitrogen
3. C
  Carbon(IV) oxide
  Correct
4. D
  Hydrogen
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Answer: C
Carbon(IV) oxide (CO₂) is the gas mainly responsible for global warming. It is released when fossil fuels (petrol, diesel, coal, gas) are burnt, and when forests are cleared and burnt. Carbon(IV) oxide traps heat radiated from the earth's surface in the atmosphere, a process called the greenhouse effect, which raises the earth's average temperature.
Nitrogen and oxygen make up about 99% of the atmosphere but do not trap heat in this way, so they are not greenhouse gases. Hydrogen is not naturally present in the atmosphere in any significant amount and plays no role in global warming.
This is why carbon(IV) oxide, not the other choices, is correct.
10.
The enzyme that converts glucose to ethylalcohol is?
1. A
  Invertase
2. B
  Zymase
  Correct
3. C
  Diastase
4. D
  Maltase
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Answer: B
In the fermentation of carbohydrates by yeast, several enzymes act in sequence, but only one actually produces the alcohol.
Zymase is the enzyme (enzyme complex) that acts directly on glucose, converting it into ethyl alcohol (ethanol) and carbon dioxide:
C6H12O6 → 2C2H5OH + 2CO2
This is the final and defining step of alcoholic fermentation, so zymase is correct.

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JAMB Chemistry 2021 past questions

JAMB Chemistry 2021 questions and answers

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