Most Repeated MDCAT Chemistry MCQs

1. 1

   Repeated 7×Carboxylic Acids and its Derivatives

   Which one of the following is strongest acid?

   • ACH3COOH
   • BCH3CH2COOH
   • CC6H5CG2COOH
   • DFCH2COOH✓

   Explanation

   D is the correct option, as it contains a halogen which have strong electron-withdrawing effects.

   Appeared in past papers: 2009, 2011, 2013

2. 2

   Repeated 9×Chemical Bonding

   Linear combination of atomic orbitals (LCAO) results in the formation of:

   • ASigma bond
   • BPi bond
   • CBonding molecular orbitals only
   • DBonding and antibonding molecular orbitals✓
   • EAll of these options

   Explanation

   According to Molecular Orbital Theory (MOT), two atomic orbitals overlap resulting in the formation of molecular orbitals. Number of atomic orbitals overlapping together is equal to the molecular orbital formed. The two atomic orbital thus formed by LCAO (linear combination of atomic orbital) in the same phase or in the different phase are known as Bonding Molecular Orbital (BMO) and Antibonding Molecular Orbitals (ABMO) respectively.

   Appeared in past papers: 2010

3. 3

   Repeated 7×Miscellaneous

   For the reaction N2+ 3H2 —-->2NH3 The production of NH3 will be favored at:

   • AHigh pressure and catalyst✓
   • BLow pressure only
   • CLow pressure and catalyst
   • DHigh pressure only
   • ECatalyst only

   Explanation

   When pressure is applied on a system that contains gasses then the reaction will shift in the direction that contains less number of molecules. High Pressure will shift the reaction towards the right-hand side which is favored to attain more product and Catalyst helps to obtain a new equilibrium faster.

   Appeared in past papers: 2009, 2010

4. 4

   Repeated 9×Atomic Structure

   The maximum number of electrons that an orbital can accommodate is/are:

   • A0
   • B1
   • C2✓
   • D3
   • E4

   Explanation

   The maximum number of electrons in a single orbital is two. The maximum number of electrons an orbital can accommodate is 2. As in an orbital two electrons can never have the same values of all 4 quantum no.s according to Pauli’s exclusion principle. So to follow this rule, an orbital can accommodate 2 electrons only.

   Appeared in past papers: 2009, 2010

5. 5

   Repeated 9×Chemical Bonding

   If the difference between electronegativity values between two atoms is less than 1.7, the bond is necessarily.

   • ACovalent✓
   • BIonic
   • CPolar covalent
   • DMetallic

   Explanation

   This is the correct answer. When the electronegativity difference between two atoms is less than 1.7, the bond formed between them is generally considered covalent. In a covalent bond, the atoms share electrons to achieve a stable electron configuration.

   Appeared in past papers: 2016, 2023

6. 6

   Repeated 9×S 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 past papers: 2018, 2023

7. 7

   Repeated 8×Miscellaneous

   Alcohol in which carbon atom bonded to OH group is further attached with three alkyl group is:

   • ATertiary alcohol✓
   • BPrimary alcohol
   • CAromatic alcohol
   • DSecondary alcohol

   Explanation

   A tertiary (3°) alcohol is one in which the carbon atom with the OH group is attached to three other carbon atoms. Its general formula is R3COH Primary alcohols are those alcohols where the carbon atom of the hydroxyl group (OH) is attached to only one single alkyl group. The aromatic alcohols or aryl-alcohols are a class of chemical compounds containing a hydroxyl group (—OH) bonded directly to an aromatic hydrocarbon group. A secondary alcohol is a compound in which a hydroxyl group( ‒OH) is attached to a saturated carbon atom which has two other carbon atoms attached to it.

   Appeared in past papers: 2018

8. 8

   Repeated 8×Thermochemistry

   Which enthalpy change is relevant in the following process Na(s) → Na (g) ΔH = +107

   • AEnthalpy of atomization✓
   • BEnthalpy of fusion
   • CEnthalpy of vaporization
   • DEnthalpy of formation

   Explanation

   Option A, enthalpy of atomization, is the energy required to completely separate all the atoms in a chemical substance. The separated atoms are in a gaseous state and get separated from the corresponding substance in its standard state. Sodium is solid in its standard state, and after atomization, the atoms are in their gaseous state. Hence, this is the correct answer. Option B is the enthalpy change when a solid substance melts into a liquid. Here, the state change is from a solid to a gas, no liquid state involved. Option C is the enthalpy change when a liquid is vaporized into a gas. Here,

   Appeared in past papers: 2019

9. 9

   Repeated 8×Thermochemistry

   Reaction of water with quicklime results in the rise in the temperature of the system. Using the concept of an energy change, indicates the nature of the reaction?

   • AEndothermic Reaction
   • BNon-Spontaneous Reaction
   • CThird Order Reaction
   • DExothermic Reaction✓

   Explanation

   Calcium oxide reacts with water to form calcium hydroxide, also called slaked lime. Here are the for this reaction: Calcium oxide + water → calcium hydroxide CaO+H2O → Ca(OH)2 A lot of heat is produced in the reaction, which may even cause the water to boil. Hence it is a combination reaction as well as exothermic reaction.

   Appeared in past papers: 2018

10. 10

    Repeated 8×Chemical Bonding

    Which option shows all the molecules with bond angle 109.5 degrees:

    • ACH4 , NH4+ , PH3
    • BSiCl4 , H2O , BeCl2
    • CSiCl4 , NH4+ , CH4✓
    • DCH4 , CCl4 , NH3

    Explanation

    Since all molecules stated in option C are tetrahedral in shape, where a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. Hence they all have bond angles that are 109.5 degrees.

    Appeared in past papers: 2018

11. 11

    Repeated 8×Aldehydes and Ketones

    Select the reagent X from the following choices for this conversion:

    • AAcidified Potassium hydroxide
    • BAcidified Potassium dichromate (VI)✓
    • CAcidified Phosphoric acid
    • DAcidified Oxalic acid

    Explanation

    The reaction above is oxidation of a secondary alcohol into a ketone. As such, an oxidizing agent must be chosen for reagent X. Among the options, 'Potassium dichromate (VI)' is an oxidizing agent so, the correct option is B. Another answer could be 'potassium manganate (VII)', but it is not mentioned in any of the options. The other options do not oxidize alcohols.

    Appeared in past papers: 2019

12. 12

    Repeated 8×Chemical Bonding

    The raindrop acquires a spherical shape and ink spread over blotting paper due to:

    • ASurface tension✓
    • BAdhesive forces
    • CViscosity
    • DPolarity
    • ELatent heat of vaporization

    Explanation

    A raindrop falling through the atmosphere forms a roughly spherical structure due to the surface tension of water. This surface tension is the “skin” of a body of water that makes the molecules stick together. The cause is the weak hydrogen bonds that occur between water molecules.

    Appeared in past papers: 2010

13. 13

    Repeated 7×Alkyl Halides and Amines

    Which of the following is not a nucleophile?

    • ANH3
    • BOH
    • CCN-
    • DBr2✓

    Explanation

    Br₂ is not a nucleophile because:No Significant Negative Charge:Nucleophiles are electron-rich species that donate electrons.Br₂ is a neutral molecule with no formal negative charge, making it less likely to donate electrons.Weak Electron Donation Ability:Even though Br atoms have lone pairs, they are held tightly and not readily available for donation.Instead, Br₂ tends to act as an electrophile (electron acceptor), especially in reactions like electrophilic addition.Polarizability but No Strong Nucleophilic Character:Br₂ is a polarizable molecule, meaning it can momentarily develop dipoles,

    Appeared in past papers: 2009, 2010

14. 14

    Repeated 8×Acids, 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 past papers: 2010, 2017

15. 15

    Repeated 8×Alcohols, Phenols and Ether

    Primary Alcohol is produced by reactions of Grignard's reagent with _ followed by hydrolysis in an acidic medium.

    • ACarbon dioxide
    • BFormaldehyde✓
    • CAcetaldehyde
    • DKetone
    • EMethyl chloride

    Explanation

    The Grignard Reaction involves the addition of an organomagnesium halide (Grignard reagent) to carbonyl compounds. When Grignard reagents react with formaldehyde, a primary alcohol is produced upon hydrolysis in an acidic medium. Formaldehyde is unique as it is the simplest aldehyde, thus allowing the formation of a primary alcohol. Other aldehydes and ketones lead to secondary and tertiary alcohols, respectively. Carbon dioxide reacts with Grignard reagents to form carboxylic acids, not alcohols, and methyl chloride does not react to form an alcohol.

    Appeared in past papers: 2011

16. 16

    Repeated 8×Miscellaneous

    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 ato

    Appeared in past papers: 2023

17. 17

    Repeated 7×Aldehydes and Ketones

    Which type of reaction takes place when a carbonyl compound is treated with a mixture of NaCN and an acid?

    • AElectrophilic addition reaction
    • BSubstitution reaction
    • CNucleophilic addition reaction✓
    • DDisplacement reaction

    Explanation

    The given scenario is an example of a nucleophilic addition reaction, as the reactant, CN- is a nucleophile which adds across the carbonyl bond. Option A describes reactions undergone by alkenes, where an electrophile is added across the carbon-carbon double bond. Option B describes a reaction where one group of atoms is replaced by another group of atoms, but this is not the case here. Option D describes a reaction in which one element is replaced by another element in a compound.

    Appeared in past papers: 2019

18. 18

    Repeated 7×Carboxylic Acids and its Derivatives

    Which of the following catalysts is used in the below reaction?

    • AConc. H2SO4✓
    • BPurnice stone
    • CPt
    • DNi

    Explanation

    Esterification process is a slow process when it is performed at room temperature also the process does not complete at all in the room temperature. So to complete the process of esterification there should be something to complete the process as well as to speed up the process. Thus concentrated sulphuric acid is added. It is a catalyst which will speed up the process and esterification will proceed speedily and complete on time. Also concentrated sulphuric acid has a property to remove water. Therefore it also acts as a dehydrating agent. After adding this will take reaction in the equilibri

    Appeared in past papers: 2018

19. 19

    Repeated 7×Thermochemistry

    The enthalpy change accompanying the gain of an electron by a neutral gaseous atom to form a negative ion is called:

    • AIonization potential
    • BElectronegativity
    • CElectron affinity✓
    • DLattice energy
    • EPotential energy

    Explanation

    When an electron is added to a neutral gaseous atom to convert it into a negative ion, the enthalpy change accompanying the process is called Electron affinity enthalpy. Ionization potential, in chemistry, is the amount of energy required to remove an electron from an isolated atom or molecule. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. Lattice energy is defined as the energy required to separate a mole of an ionic solid into gaseous ions. Potential energy is energy that is stored – or conserved - in an object or substance.

    Appeared in past papers: 2010

20. 20

    Repeated 7×Hydrocarbons

    Catenation is a process in which carbon shows the properties of:

    • AMaking single bond
    • BHybridization
    • CMaking chains or rings of carbon atoms✓
    • DIsomerism
    • EBreaking of bonds

    Explanation

    Catenation is the process by which an atom is able to form a bond with another atom of its kind. Carbon possesses this ability hence is able to form ringed structures.

    Appeared in past papers: 2010

21. 21

    Repeated 7×Thermochemistry

    Which of the following values of heat of formation indicates that the product is least stable?

    • A- 94 kcal
    • B+ 21.4 kcal
    • C- 231 kcal
    • D+ 64.8 kcal✓

    Explanation

    In the context of heat of formation (ΔH), a negative value indicates that the formation of the compound is exothermic, meaning the compound is more stable compared to its constituent elements in their standard states.So, the least stable compound among the options provided would have the most positive (ΔH) value and option d has the most positive value ,hence that is the correct option.

    Appeared in past papers: 2017

22. 22

    Repeated 7×Alkyl Halides and Amines

    Which alkyl halide has the lowest reactivity for a particular alkyl group?

    • AR-F✓
    • BR-Cl
    • CR-Br
    • DR-I

    Explanation

    This is the correct answer. Alkyl halides are compounds in which a halogen atom (F, Cl, Br, or I) is bonded to a carbon atom. The reactivity of alkyl halides generally increases in the order R-F < R-Cl < R-Br < R-I. This trend is due to the decreasing bond strength between the carbon atom and the halogen atom as the size of the halogen increases.

    Appeared in past papers: 2018, 2023

23. 23

    Repeated 7×Hydrocarbons

    Which of the following substitutents is an Ortho and Para director and ring deactivating?

    • A–OH
    • B–NH2
    • C–Cl✓
    • D–OCH3

    Explanation

    In electrophilic aromatic substitution, the nature of the substituent on the benzene ring plays a crucial role in determining the position of new substituents and the reactivity of the ring. Ortho-para directors are groups that direct incoming electrophiles to the 2, 4 (ortho, para) positions. While most ortho-para directors are activating, -Cl is an exception as it directs due to resonance but deactivates due to a strong inductive effect. This means it reduces the overall reactivity of the benzene ring but still allows for substitution at ortho and para positions.In contrast, –OH and –NH2 gro

    Appeared in past papers: 2014

24. 24

    Repeated 7×Hydrocarbons

    Which of the following compounds undergo nitration most readily?

    • ABenzene
    • BToluene✓
    • CBenzoic acid
    • DNitrobenzene

    Explanation

    The correct answer is Toluene. Toluene undergoes nitration much faster than benzene due to the presence of a methyl group. This group donates electron density to the ring, particularly enhancing the reactivity at the ortho and para positions, making the electrophilic aromatic substitution process more favorable.Why the other options are incorrect:Benzene: While benzene can undergo nitration, it lacks activating groups, making it less reactive compared to toluene.Benzoic Acid: The carboxyl group is a deactivating group, reducing electron density in the ring and hindering electrophilic attack.Ni

    Appeared in past papers: 2014

25. 25

    Repeated 7×Chemical Bonding

    Which one of the following is most ionic?

    • ANaCl
    • BMgCl2
    • CKCl✓
    • DAlCl3

    Explanation

    The correct answer is KCl because it forms the most ionic bond among the options provided. Potassium (K) is larger and has a lower charge density than sodium (Na), making it easier to lose its valence electron and form a K+ cation. According to Fajan's rules, larger cations with a lower charge density form more ionic bonds, which is why KCl is more ionic than NaCl. NaCl is ionic, but sodium's smaller size compared to potassium leads to a slightly higher charge density, resulting in less ionic character compared to KCl.MgCl2 has a +2 charge on magnesium, which increases the covalent character o

    Appeared in past papers: 2014

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