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Most Repeated MDCAT Chemistry MCQs
Chemistry carries 25% of your MDCAT — 45 of the 180 marks — so a handful of recurring concepts can swing your whole score. This page lists the 25 most repeated Chemistry MCQs, pulled straight from Premeth's corpus of 377 real past papers and 40,659 core-subject questions across Punjab/UHS, Sindh, ETEA/KPK, Federal and Balochistan.
Our rule is deliberately strict: a question counts as "most repeated" only when the same correct answer shows up across 2 or more different exam years. These aren't guesses or predicted questions — they're genuine cross-exam repeats measured from the real papers. The clearest example is the classic bonding item, "LCAO results in the formation of → Bonding and antibonding molecular orbitals," which recurs multiple exam years.
The heaviest repeat clusters sit in Chemical Bonding, Thermochemistry, and Hydrocarbons — so if you're short on time, these are the topics that reward revision the most.
Measured from 377 real past papers · updated July 2026
Treat this list as a priority filter, not a shortcut. Read each question, cover the answer, and try to reason it out before checking — for a repeat like the LCAO item, you want to understand why LCAO produces bonding and antibonding orbitals, because examiners reword the same concept across papers. If you can only explain the answer by memorising it, you'll miss the rephrased version.
Work top-down by cluster: nail Chemical Bonding, Thermochemistry and Hydrocarbons first, since that's where repeats concentrate, then use your NCERT/board Chemistry text to fill any concept you couldn't justify. With no negative marking on MDCAT 2026, these high-frequency topics are exactly where you lock in safe, fast marks on 16 August.
Most-repeated Chemistry chapters
Each chapter below has its own page of most-repeated questions — with verified answers, explanations and the exact exam years each recurred in. Ranked by how many of its questions recur across 2+ years.
| # | Chapter | Repeated questions | Frequency |
|---|---|---|---|
| 1 | Aldehydes and Ketones | 12 | |
| 2 | States of Matter - Gases, Liquids and Solids | 11 | |
| 3 | Chemical Bonding | 11 | |
| 4 | Fundamental Principles of Organic Chemistry | 11 | |
| 5 | Atomic Structure | 11 | |
| 6 | D and f Block Elements | 10 | |
| 7 | Hydrocarbons | 10 | |
| 8 | Alkyl Halides and Amines | 9 | |
| 9 | Alcohols, Phenols and Ether | 8 | |
| 10 | Chemical Equilibrium | 8 |
More repeated Chemistry questions
Repeated Chemistry questions from chapters that don't yet have their own page — each with the verified answer, explanation and the years it recurred.
- 1Repeated in 3 yearsFSc Qbank
Which of the following is a typical transition metal?
- ASc
- BY
- CCo✓
- DRa
Explanation
Group IIB elements (Zn, Cd and Hg) do not have a partially filled d-subshell either as elements or in any of their ionic state. Neither do they show typical properties of transition elements to any appreciable extent (except complex formation). Similarly, IIIB (Sc, Y and La) is another group of elements which do not show many of the properties associated with typical transition elements.
Appeared in the past papers of: 2010, 2015, 2017
- 2Repeated in 3 yearsEnvironmental Chemistry
Ecosystem is a smaller unit of:
- ALithosphere
- BHydrosphere
- CBiosphere✓
- DAtmospheric
Explanation
Biosphere is the region of earth capable of supporting life. It includes lower atmosphere, the oceans, rivers, lakes, soils and solid sediments that actively interchange materials with all types of living organisms i.e., human beings, animals and plants. Ecosystem is a smaller unit of biosphere which consists of community of organisms and their interaction with environment i.e.
Appeared in the past papers of: 2016, 2017, 2018
- 3Repeated in 3 yearsMiscellaneous
What is the proton (atomic number) of an element that has four unpaired electrons in its ground state?
- A6
- B14
- C22
- D26✓
Explanation
The number of unpaired electrons in an element's ground state corresponds to the element's atomic number, which is the number of protons in its nucleus. In this case, an element with four unpaired electrons would have an atomic number of 26.
Appeared in the past papers of: 2022, 2023, 2024
- 4Repeated in 3 yearsMiscellaneous
One can estimate the direction in which equilibrium will shift with the help of:
- ALe Chatelier's principle✓
- BLaw of mass action
- CHess's law
- DLaw of heat of formation
Explanation
Le-Chatelier's principle is a concept that helps in predicting the direction in which a system at equilibrium will shift in response to a change in conditions.
Appeared in the past papers of: 2022, 2023, 2024
- 5Repeated in 3 yearsMiscellaneous
If carboxylic acid and ketone groups C=O are present in a chain then final name will be given as
- Aoxo, oic acid✓
- Bone, oic acid
- CBoth 1 and 2
- DNone of these
Explanation
The naming convention for compounds containing both a carboxylic acid group and a ketone group involves using the prefix "oxo" to indicate the presence of the ketone group, followed by the name of the alkyl chain attached to the carboxylic acid group, and ending with the suffix "oic acid" to denote the carboxylic acid group.
Appeared in the past papers of: 2022, 2023, 2024
- 6Repeated in 3 yearsAcids, Bases and Salts
Which of the following statements about H2S is false:
- AIt is a covalent compound
- BIt is a gas with a bad smell
- CIt is a strong reducing agent
- DIt is a molecule which is non linear
- EIt is a weak base in water✓
Explanation
H2S is a weak acid, donating two hydrogen ions in neutralization reactions, forming HS- and S-2 ions, not a weak base. Hence option E is the correct answer.H2S is a covalent compound with a rotten egg smell. It is a strong reducing agent with a bent (non-linear) geometry.
Appeared in the past papers of: 2009, 2010, 2017
- 7Repeated in 3 yearsMiscellaneous
The crystals formed as a result of Van Der Waals interactions are:
- AMolecular crystals✓
- BCovalent crystals
- CMetallic crystals
- DIonic crystals
- ENone of the above
Explanation
Crystal in which molecules are bonded through weak forces called Van Der Waals forces.
Appeared in the past papers of: 2009, 2013, 2016
- 8Repeated in 3 yearsS and p Block Elements
Lithium and beryllium are unique in such a way that they have higher charge densities which produce strong polarizing effects due to:
- ASmall size✓
- BHigh electronegativity
- CLow ionization energy
- DLarge atomic radius
Explanation
This is the correct answer. Lithium and beryllium have smaller atomic radii compared to other elements in their respective groups. This small size combined with their relatively high positive charges (Li+ and Be2+) results in a high charge density. This high charge density allows them to exert strong polarizing effects on the electron clouds of neighboring atoms or ions, leading to the formation of covalent bonds or polar covalent bonds.Therefore, the unique properties of lithium and beryllium, including their strong polarizing effects, are primarily due to their small size.
Appeared in the past papers of: 2018, 2023, 2024
- 9Repeated in 3 yearsKingdom Animalia
The normal pH of blood is:
- A7.05
- B7.75
- C7.35✓
- D7.25
Explanation
The normal pH of human blood is slightly basic, around 7.35– 7.45. This pH is maintained by buffer systems like bicarbonate to ensure proper enzyme and metabolic function. A deviation can lead to acidosis or alkalosis, affecting body processes.
Appeared in the past papers of: 2018, 2023, 2024
- 10Repeated in 3 yearsMiscellaneous
The total energy of a hydrogen atom in its ground state is:
- AZero
- BNegative✓
- CPositive
- DNone of the above
Explanation
The total energy of a hydrogen atom in its ground state can be calculated using the Schrödinger equation, which is a fundamental equation in quantum mechanics. The ground state of a hydrogen atom refers to the lowest energy state that the electron can occupy. In the Bohr model of the hydrogen atom, the ground state energy can be expressed as: E = -13.6 eV / n2 Where: E is the energy of the ground state in electron volts (eV), n is the principal quantum number, which is equal to 1 for the ground state. Plugging in the values: E = -13.6 eV / (12) = -13.6 eV So, the total energy of a hydrogen atom in its ground state is approximately -13.6 electron volts.
Appeared in the past papers of: 2008, 2016, 2023
- 11Repeated in 2 yearsFSc Qbank
Which compound is the most reactive one?
- ABenzene
- BEthyne
- CEthene✓
- DEthane
Explanation
The unreactivity of alkanes can also be explained on the basis of inertness of a s-bond. In a s -bond the electrons are very tightly held between the nuclei which makes it a very stable bond. A lot of energy is required to break it. A pi-bond is, therefore, a weak bond as compared to a s-bond. During a reaction it breaks comparatively easily rendering alkenes as reactive group of compounds. In alkynes, the carbon atoms are held together by a triple bond, a s-bond and two p-bonds. The electron density between the carbon atoms is very high which draws atoms very close to each other.
Appeared in the past papers of: 2009, 2015
- 12Repeated in 2 yearsFSc Qbank
Ethanol can be converted into ethanoic acid by:
- AHydrogenation
- BHydration
- COxidation✓
- DFermentation
Explanation
Ethanol can be oxidized to form ethanoic acid. This process typically involves the use of an oxidizing agent such as potassium dichromate (K2Cr2O7) or potassium permanganate (KMnO4) in the presence of an acidic medium.
Appeared in the past papers of: 2016, 2019
- 13Repeated in 2 yearsFSc Qbank
Ketones are prepared by oxidation of:
- Aprimary alcohol
- Bsecondary alcohol✓
- Ctertiary alcohol
- Dphenol
Explanation
The oxidation of alcohols is an important reaction in organic chemistry. Primary alcohols can be oxidized to form aldehydes and carboxylic acids; secondary alcohols can be oxidized to give ketones. Tertiary alcohols, in contrast, cannot be oxidized without breaking the molecule's C–C bonds.
Appeared in the past papers of: 2017, 2023
- 14Repeated in 2 yearsFSc Qbank
For which mechanism the first step involved is the same?
- AE1 and E2
- BE2 and SN2
- CSN2 and E2
- DE1 and SN1✓
Explanation
In E1 mechanism, like SN1 mechanism, the first step is the slow ionization of the substrate to give a carbocation. In the second step, the nucleophile attacks on hydrogen to give an alkene as a product.
Appeared in the past papers of: 2016, 2023
- 15Repeated in 2 yearsFSc Qbank
Laughing gas is chemically
- ANO
- BN2O✓
- CNO2
- DN2O4
Explanation
Nitrous oxide is an oxide of nitrogen with a chemical formula N2O. This organic compound is colourless and non-flammable at room temperature. It is also known as nitrous or laughing gas.
Appeared in the past papers of: 2017, 2019
FAQs
What are the most repeated MDCAT Chemistry MCQs?
They are Chemistry questions whose same correct answer has appeared in 3 or more separate MDCAT past papers. This page shows the top 25, with the heaviest repeats clustering in Chemical Bonding, Thermochemistry and Hydrocarbons.
How were these 'most repeated' questions identified?
By scanning Premeth's corpus of 377 real past papers and 40,659 core-subject questions across UHS/Punjab, Sindh, ETEA/KPK, Federal and Balochistan, then counting only questions where the same correct answer recurred across 3+ papers. They are measured repeats, not predictions.
How much of the MDCAT is Chemistry?
Chemistry is 25% of the paper — 45 of the 180 MCQs. Biology is 45%, Physics 20%, English 5% and Logical Reasoning 5%. MDCAT 2026 is on 16 August 2026, with 180 MCQs in 180 minutes and no negative marking.
Which Chemistry topics repeat most on MDCAT?
The strongest repeat clusters are Chemical Bonding, Thermochemistry and Hydrocarbons. A standout example is 'LCAO results in the formation of → Bonding and antibonding molecular orbitals,' which appears multiple exam years across past papers.
Are these the exact questions that will come in MDCAT 2026?
No. This is honest past-paper frequency data, not a leak or a prediction of the 2026 paper. But because these concepts have repeated across many real exams, they're the highest-value topics to master before the test.
Do these repeats apply to all boards, or just UHS/Punjab?
The corpus spans Punjab/UHS, Sindh, ETEA/KPK, Federal and Balochistan papers, so the repeat counts reflect cross-board frequency. The concepts that recur tend to be core syllabus topics that show up regardless of which board's paper you sit.