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Punjab Chemistry 2021 Paper 2 — Solved Past Paper with Answers
All 17 MCQs from Punjab Chemistry 2021 Paper 2, solved with the correct answer highlighted and a full explanation for every question. This is a free MDCAT Punjab / UHS past paper — no signup, no ads. Practise it interactively in timed mode, drill more with free MDCAT MCQs, or browse all Punjab / UHS papers.
Attempt this paper interactively →Q1. Each of second and third periods contain elements:
- A. 2
- B. 18✓
- C. 8
- D. 32
Explanation: This refers to the third period of the periodic table, which contains 8 elements (from Sodium (Na) to Argon (Ar)).
Why the other options are wrong
- A. This refers to the second period of the periodic table, which contains only 2 elements: Lithium (Li) and Beryllium (Be).
- C. This refers to the number of groups in the periodic table, but it's not specifically related to the second or third periods.
- D. It's not directly related to any specific period or group in the periodic table.
Q2. Which one of the following does not belong to Alkaline earth metals?
- A. Be
- B. Ra
- C. Ba
- D. Rn✓
Explanation: Radon is a chemical element with the symbol Rn and atomic number 86. It is a noble gas, not an alkaline earth metal. Radon is a radioactive gas that is colorless, odorless, and tasteless. It is formed as a decay product of uranium and thorium in the Earth's crust. Radon is known for being a health hazard due to its radioactivity and potential to accumulate in enclosed spaces.
Why the other options are wrong
- A. Beryllium is a chemical element with the symbol Be and atomic number 4. It belongs to the alkaline earth metals group in the periodic table. Beryllium is a lightweight, strong, and brittle alkaline earth metal.
- B. Radium is a chemical element with the symbol Ra and atomic number 88. It is an alkaline earth metal that is radioactive. Radium is formed as a decay product of uranium and thorium ores.
- C. Barium is a chemical element with the symbol Ba and atomic number 56. It is an alkaline earth metal that is soft, silvery-white, and reactive. Barium compounds are used in various industries, including the production of glass, ceramics, and fireworks.
Q3. Which metal is used in Thermite Process because of its reactivity?
- A. Iron
- B. Copper
- C. Aluminium✓
- D. Zinc
Explanation: Aluminium is a chemical element with the symbol Al and atomic number 13. It is the metal commonly used in the thermite process due to its high reactivity. When powdered aluminium reacts with metal oxides, such as iron oxide (Fe2O3), an exothermic reaction occurs, producing molten metal and releasing a significant amount of heat.
Why the other options are wrong
- A. Iron is a chemical element with the symbol Fe and atomic number 26. While iron is reactive, it is not typically used in the thermite process as the reactive metal.
- B. Copper is a chemical element with the symbol Cu and atomic number 29. Copper is not commonly used in the thermite process due to its lower reactivity compared to other metals.
- D. Zinc is a chemical element with the symbol Zn and atomic number 30. While zinc is reactive, it is not commonly used in the thermite process.
Q4. All the elements of VI A are non-metals except:
- A. Se
- B. Po✓
- C. S
- D. Te
Explanation: Polonium is a metalloid. It is the only non-metal in Group 16, making it an exception among the elements listed. Polonium exhibits some properties of metals, such as conductivity, but also displays characteristics of non-metals.
Why the other options are wrong
- A. Selenium is a non-metal. It is a member of Group 16 (also known as Group VI A) of the periodic table, which consists mainly of non-metals.
- C. Sulfur is a non-metal. Like selenium, it belongs to Group 16 of the periodic table and shares typical non-metallic properties.
- D. Tellurium is a metalloid. It is another member of Group 16 and shares some properties with both metals and non-metals.
Q5. The anhydride of HCIO4 is:
- A. CIO3
- B. CIO2
- C. C*l2*O5
- D. C*l2*O7✓
Explanation: This is the correct anhydride of perchloric acid (HClO₄). It is formed when perchloric acid loses water (H₂O), leaving behind the anhydride, dichlorine heptoxide.
Why the other options are wrong
- A. This compound is not the anhydride of perchloric acid (HClO₄). Chlorine trioxide is a distinct compound with a different chemical formula and properties.
- B. Similarly, chlorine dioxide is not the anhydride of perchloric acid. It is a separate compound with its own chemical characteristics.
- C. This compound is also not the anhydride of perchloric acid. Dichlorine pentoxide is a different substance with its own formula and properties.
Q6. The electron affinity values of halogens are:
- A. Large and Positive
- B. Large and Negative✓
- C. Small and Positive
- D. Small and Negative
Explanation: Halogens have large negative electron affinities, meaning they release a significant amount of energy when gaining an electron.
Why the other options are wrong
- A. Electron affinity refers to the energy released when an electron is added to a neutral atom. Halogens have a high electron affinity because they readily gain an electron to achieve a stable electron configuration. However, this energy release is typically negative, indicating that energy is released during the process.
- C. Small and positive electron affinities would imply that the halogens do not readily gain electrons and may even lose them, which contradicts their behavior.
- D. Halogens have relatively large negative electron affinities, indicating their strong tendency to gain an electron.
Q7. Which of the following is a non-typical Transition element?
- A. Cr
- B. Mn
- C. Zn✓
- D. Fe
Explanation: Zinc is not considered a typical transition element because it lacks partially filled d orbitals in its neutral or common oxidation states. It typically exhibits a +2 oxidation state, with a completely filled d orbital, resembling more like an s-block element in terms of electronic configuration.
Why the other options are wrong
- A. Chromium is a transition metal commonly found in the d-block of the periodic table. It exhibits typical transition metal properties, including multiple oxidation states and the ability to form complex ions.
- B. Manganese is also a transition metal and displays typical transition metal characteristics. It forms various oxidation states and can participate in the formation of complex ions.
- D. Iron is a classic example of a transition metal. It exhibits multiple oxidation states and forms complex ions. Iron is commonly found in the d-block of the periodic table.
Q8. Ether show the phenomenon of:
- A. Positive Isomerism
- B. Metamerism✓
- C. Functional group Isomerism
- D. Cis-trans isomerism
Explanation: Metamerism is a type of structural isomerism where compounds have the same functional groups but differ in the nature or number of atoms within the chain connecting the functional groups. Ether compounds often exhibit metamerism when the alkyl groups on either side of the oxygen atom differ.
Why the other options are wrong
- A. There's no such phenomenon as "Positive Isomerism." Isomerism refers to the existence of molecules with the same molecular formula but different structural arrangements or spatial orientations.
- C. Functional group isomerism occurs when compounds with the same molecular formula have different functional groups. This is not typically observed in ethers, as ethers generally contain the same functional group (-O-), differing mainly in the alkyl groups attached to the oxygen atom.
- D. Cis-trans isomerism, also known as geometric isomerism, occurs when atoms or groups of atoms are arranged differently around a rigid structure, often a double bond or a ring. Ethers do not typically exhibit cis-trans isomerism because they lack such rigid structures.
Q9. Which one of the following gases is used for artificial ripening of fruits?
- A. Ethene✓
- B. Ethane
- C. Methane
- D. Propane
Explanation: Ethene is commonly used for the artificial ripening of fruits. It is a plant hormone that triggers the ripening process in fruits. When fruits are exposed to ethene gas, it stimulates the production of enzymes responsible for ripening, such as cellulase and pectinase.
Why the other options are wrong
- B. Ethane is not typically used for fruit ripening. It is a simple hydrocarbon gas and does not have the ripening-inducing properties of ethene.
- C. Methane is not used for fruit ripening. It is a flammable gas and is primarily used as a fuel or for industrial processes.
- D. Propane is also not used for fruit ripening. Like methane, it is primarily used as a fuel and is not involved in the ripening process of fruits.
Q10. Benzene cannot undergo:
- A. Substitution reactions
- B. Addition reactions
- C. Oxidation reactions
- D. Elimination reactions✓
Explanation: Due to presence of pi-bonds benzene can not under go elimination reaction.
Why the other options are wrong
- A. The presence of the delocalised π-electrons makes benzene particularly stable. Benzene resists addition reactions because that would involve breaking the delocalisation and losing that stability.
- B. The presence of the delocalised π-electrons makes benzene particularly stable. Benzene resists addition reactions because that would involve breaking the delocalisation and losing that stability.
- C. Benzene (C6H6) is a hydrocarbon that is resistant to oxidation under normal conditions. In aqueous solution, benzene is not soluble and does not undergo oxidation reactions.
Q11. Which one of the following is not a Nucleophile?
- A. H2*O
- B. H2*S
- C. B*F3✓
- D. N*H3
Explanation: Boron trifluoride is not typically considered a nucleophile. It is often used as a Lewis acid, meaning it can accept a pair of electrons from a nucleophile. In some cases, it can act as a catalyst or a reaction promoter by facilitating bond formation between other molecules, but it does not act as a nucleophile itself.
Why the other options are wrong
- A. Water can act as a nucleophile in certain reactions, particularly in substitution and addition reactions where it donates a lone pair of electrons to form a new bond with an electrophilic atom or molecule. This lone pair makes water a potential nucleophile.
- B. Similar to water, hydrogen sulfide can also act as a nucleophile in various chemical reactions. It has a lone pair of electrons on the sulfur atom, allowing it to donate electrons to form bonds with electrophiles.
- D. Ammonia is a well-known nucleophile. It has a lone pair of electrons on the nitrogen atom, which it can donate in chemical reactions to form new bonds with electrophiles. This makes ammonia capable of participating in various nucleophilic substitution and addition reactions.
Q12. Which compound shows hydrogen bonding?
- A. C2*H6
- B. C2*H5*Cl
- C. CHOSCH
- D. C2*H5*OH✓
Explanation: Ethanol contains carbon, hydrogen, and oxygen atoms. The hydrogen atoms in ethanol are directly bonded to an oxygen atom. Oxygen is highly electronegative, creating a large dipole moment between the hydrogen and oxygen atoms. This polarity allows ethanol molecules to form hydrogen bonds with each other, making ethanol the correct option.
Why the other options are wrong
- A. Ethane consists only of carbon and hydrogen atoms bonded together by single covalent bonds. Hydrogen bonding occurs when hydrogen is directly bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. Since ethane lacks such atoms, it cannot exhibit hydrogen bonding.
- B. Ethyl chloride contains a chlorine atom along with carbon and hydrogen atoms. While chlorine is electronegative, it is not as electronegative as oxygen or nitrogen, which are typically involved in hydrogen bonding. Therefore, ethyl chloride does not participate in hydrogen bonding.
- C. This formula represents dimethyl sulfoxide (DMSO). DMSO contains sulfur and oxygen atoms, both of which are electronegative. However, in DMSO, the hydrogen atoms are not directly bonded to either sulfur or oxygen in a manner conducive to hydrogen bonding. Therefore, dimethyl sulfoxide does not exhibit hydrogen bonding.
Q13. Which of the following has highest boiling point?
- A. Methanal
- B. Ethanal
- C. Propanal
- D. 2-Hexanone✓
Explanation: It has the chemical formula C6H12O and consists of a six-carbon chain with an oxygen atom double bonded to one of the carbons and surrounded by hydrogen atoms. 2-Hexanone is a colorless liquid at room temperature and has a boiling point of approximately 129°C.
Why the other options are wrong
- A. It has the chemical formula CH2O and consists of one carbon atom bonded to two hydrogen atoms and an aldehyde functional group (-CHO). Methanal is a gas at room temperature and has a boiling point of -19°C.
- B. It has the chemical formula C2H4O and consists of two carbon atoms bonded to four hydrogen atoms and an aldehyde functional group (-CHO). Ethanal is a colorless liquid at room temperature and has a boiling point of 21°C.
- C. It has the chemical formula C3H6O and consists of three carbon atoms bonded to six hydrogen atoms and an aldehyde functional group (-CHO). Propanal is a colorless liquid at room temperature and has a boiling point of 49°C.
Q14. Ketones are prepared by the oxidation of:
- A. P alcohol
- B. S alcohol✓
- C. T alcohol
- D. None of these
Explanation: Primary alcohols can be oxidized to form aldehydes and carboxylic acids; secondary alcohols can be oxidized to give ketones.
Why the other options are wrong
- A. Primary alcohols can be oxidized to form aldehydes and carboxylic acids; secondary alcohols can be oxidized to give ketones.
Q15. A carboxylic acid contains:
- A. A hydroxyl group
- B. A carboxyl group✓
- C. A hydroxyl and carboxyl group
- D. A carboxyl and an aldehydic group
Explanation: B is correct because a carboxylic acid contains a carboxyl group, which consists of a carbonyl group (C=O) and a hydroxyl group (–OH) bonded to the same carbon atom.
Why the other options are wrong
- A. A is incorrect because a hydroxyl group alone does not constitute a carboxylic acid. While carboxylic acids do contain a hydroxyl group, it is specifically bonded to the carbon atom within the carboxyl group.
- C. C is incorrect because while it states that a carboxylic acid contains both a hydroxyl and a carboxyl group, it doesn't specify that these groups are bonded together in the carboxyl functional group.
- D. D is incorrect because a carboxylic acid does not contain an aldehydic group. An aldehydic group consists of a carbonyl group bonded to a hydrogen atom and is not present in carboxylic acids.
Q16. Which reagent is used to reduce a carboxylic group to an alcohol?
- A. H2/Ni
- B. H2/Pt
- C. NaBH4
- D. LiAIH4✓
Explanation: Lithium aluminum hydride (LiAlH4) is a strong reducing agent that is capable of reducing a wide range of functional groups, including carbonyl compounds (aldehydes, ketones, carboxylic acids), esters, amides, and others, to their corresponding alcohols. Therefore, option D is correct.
Why the other options are wrong
- A. This is a common reagent used for the reduction of various functional groups, including alkenes, alkynes, and carbonyl compounds (such as ketones and aldehydes). However, it is not typically used to reduce carboxylic acids to alcohols.
- B. Similar to H2/Ni, this reagent combination is commonly used for the reduction of double and triple bonds and carbonyl compounds. It is not typically used for the reduction of carboxylic acids to alcohols.
- C. Sodium borohydride (NaBH4) is a mild reducing agent commonly used to reduce carbonyl compounds, such as aldehydes and ketones, to their corresponding alcohols. However, it is not effective for the reduction of carboxylic acids to alcohols.
Q17. Micronutrients are required in quantity ranging from:
- A. 4-40 gm
- B. 6-200 kg
- C. 6-200 gm✓
- D. 4-40 kg
Explanation: This range is more reasonable, but still, it's on the higher side. Micronutrients are generally required in smaller quantities.
Why the other options are wrong
- A. This range seems too small for micronutrients. Most micronutrients are required in much smaller quantities.
- B. This range is too large. Micronutrients are needed in very small amounts, typically measured in milligrams or micrograms, not kilograms.
- D. This range is far too large. Again, micronutrients are needed in very small amounts, not kilograms.
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