Hydrocarbon Test 5

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Question 1:

What is the most basic member of the organic compounds?





Topic: Introduction to Organic Compounds

Correct Answer: B) Methane

Detailed Hint:
  • Organic compounds are primarily composed of carbon and hydrogen atoms.
  • The simplest form of these compounds is typically the one with the least number of carbon atoms.
  • Among the options given, Methane (CH4) is the simplest organic compound as it consists of just one carbon atom bonded to four hydrogen atoms.
  • Methanol, Formaldehyde, and Formic acid, although being organic compounds, have more complex structures compared to Methane.
  • Therefore, the correct answer is B, "Methane".

Question 2:

Among the following compounds, which one exhibits the highest reactivity?





Topic: Chemical Reactivity of Organic Compounds

Correct Answer: B) Ethene

Detailed Hint:
  • The reactivity of organic compounds depends largely on their molecular structure and the type of bonds they contain.
  • In this case, Ethene is more reactive than the others due to its double bond, which makes it capable of undergoing reactions that the other compounds cannot.
  • Although Benzene is reactive due to its delocalized electron cloud, it is less reactive than Ethene.
  • Ethane and Ethyne, on the other hand, are less reactive because they possess only single and triple bonds respectively.
  • Therefore, the correct answer to this question is B, "Ethene".

Question 3:

What is the correct reactivity sequence for Alkanes, Alkenes, and Alkynes?





Topic: Reactivity of Hydrocarbon Classes

Correct Answer: B) Alkenes 1 Alkynes 2 Alkanes

Detailed Hint:
  • Alkanes, alkenes, and alkynes are classes of hydrocarbons.
  • Alkenes have a higher level of reactivity due to the presence of a double bond, which can readily participate in chemical reactions.
  • Alkynes, despite having triple bonds, are less reactive than alkenes. Alkanes, having only single bonds, are the least reactive among these three.
  • Thus, the correct reactivity order is B) Alkenes 1 Alkynes 2 Alkanes.

Question 4:

What is the product obtained when Calcium Carbide reacts with water?





Topic: Reactions of Calcium Carbide

Correct Answer: A) Ethyne

Detailed Hint:
  • Calcium carbide (CaC2) reacts with water in a well-known process to produce acetylene gas, also known as Ethyne.
  • The reaction is as follows: CaC2 + 2 H2O -> C2H2 (Ethyne) + Ca(OH)2
  • The other options, Ethane, Ethene, and Ethanol, are not the products of this reaction.
  • Therefore, the correct answer to this question is A, "Ethyne".

Question 5:

Identify the term that doesn't belong with the others:





Topic: Classification of Hydrocarbons

Correct Answer: A) Aromatic

Detailed Hint:
  • Hydrocarbons are classified into two major types: aliphatic and aromatic.
  • Alkanes, alkenes, and alkynes are subcategories of aliphatic hydrocarbons, characterized by their different types of bonds: single, double, and triple respectively.
  • Aromatic hydrocarbons, on the other hand, are a distinct category that includes compounds with a specific ring structure, such as benzene.
  • Therefore, the term that doesn't belong with the others is A, "Aromatic".

Question 6:

Upon hydrolysis, Benzenetrizonide will yield three moles of which substance?





Topic: Hydrolysis of Benzenetrizonide

Correct Answer: D) Glyoxal

Detailed Hint:
  • Benzenetrizonide is a unique compound that, when hydrolyzed, forms a specific end product.
  • The reaction results in three moles of the produced substance, indicating that each benzenetrizonide molecule gives rise to three molecules of the product.
  • In this case, the product is Glyoxal, a simple dialdehyde.
  • Thus, the correct answer to this question is D, "Glyoxal".

Question 7:

Which of the following is not an isomer of an alkane with 6 carbon atoms?





Topic: Alkane Isomers

Correct Answer: D) Neopentane

Detailed Hint:
  • Alkanes are a type of hydrocarbon with single bonds only. Isomers of alkanes are compounds that have the same number of hydrogen and carbon atoms but different structures.
  • Hexane, 2,3-dimethylbutane, and 2,2-dimethylbutane are isomers with 6 carbon atoms.
  • Neopentane, however, is an isomer with 5 carbon atoms, making it the odd one out in this list.
  • As a result, the correct answer is D, "Neopentane".

Question 8:

Which of the following statement about Alkenes is incorrect?





Topic: Properties of Alkenes

Correct Answer: C) Alkenes are less reactive compared with alkanes.

Detailed Hints:
  • Alkenes are hydrocarbons that contain a carbon-carbon double bond, which includes a pi bond.
  • While alkenes may share some physical properties with alkanes, their chemical properties differ markedly due to the presence of the double bond.
  • The double bond in alkenes makes them more reactive than alkanes, not less.
  • Alkenes also readily undergo polymerization reactions.
  • Therefore, the incorrect statement in this list is C, "Alkenes are less reactive compared with alkanes".

Question 9:

Which statement about aromatic hydrocarbons is incorrect?





Topic: Aromatic Hydrocarbons

Correct Answer: A) Aromatic hydrocarbons have a pleasant aroma.

Detailed Hints:
  • Aromatic hydrocarbons have a special kind of ring structure with shared electrons among all atoms in the ring.
  • Aromatic hydrocarbons can be either monosubstituted or polysubstituted, and the term "aromatic" doesn't necessarily mean they have a pleasant smell.
  • Therefore, the incorrect statement in this list is A, "Aromatic hydrocarbons have a pleasant aroma".

Question 10:

Arrange the following compounds in decreasing order of reactivity towards electrophilic reagents: Chlorobenzene (I), benzene (II), toluene (III), phenol (IV).





Topic: Reactivity of Aromatic Compounds

Correct Answer: A) IV > III > II > I

Detailed Hints:
  • The reactivity of aromatic compounds depends on the presence of activating or deactivating groups attached to the ring.
  • Phenol (IV) is the most reactive due to its activating -OH group, followed by toluene (III) with an activating -CH3 group, then benzene (II) with no substituent, and finally chlorobenzene (I) with a deactivating -Cl group.
  • Therefore, the correct order of reactivity is IV > III > II > I.

Question 11:

Which of the following best describes the bond structure in aromatic hydrocarbons?





Topic: Bond Structure in Aromatic Hydrocarbons

Correct Answer: D) Aromatic hydrocarbons contain a sigma bond and a delocalized pi bond.

Detailed Hints:
  • Aromatic hydrocarbons have a unique structure with a delocalized cloud of electrons.
  • This structure includes sigma bonds and a delocalized pi bond, which is distributed over the entire ring.
  • Therefore, the correct answer is D, "Aromatic hydrocarbons contain a sigma bond and a delocalized pi bond".

Question 12:

Which of the following best describes the smell of acetylene?





Topic: Characteristic Smell of Acetylene

Correct Answer: C) Acetylene smells like garlic.

Detailed Hint:
  • Acetylene is known for its use in welding and metal cutting, but it can have a distinctive smell due to impurities like phosphine, PH3.
  • This impurity gives acetylene a smell similar to garlic.
  • Therefore, the correct answer is C, "Acetylene smells like garlic".

Question 13:

Which of the following groups deactivates the benzene ring for electrophilic substitution but directs the reaction at ortho and para positions?





Topic: Deactivation and Direction of Electrophilic Substitution

Correct Answer: B) -Cl

Detailed Hints:
  • The reactivity of a benzene ring can be altered by the presence of substituents.
  • The -NH2 group is activating, -NO2 is deactivating, and -C2H5 is activating.
  • The -Cl group, while deactivating, directs the electrophilic substitution at the ortho and para positions.
  • Therefore, the correct answer is B, "-Cl".

Question 14:

Which of the following best describes alkanes?





Topic: Properties of Alkanes

Correct Answer: D) Alkanes are represented by the general formula CnH2n.

Detailed Hint:
  • Alkanes are saturated hydrocarbons with all carbon-carbon bonds being single bonds.
  • While they are also known as paraffin, the general formula for alkanes is CnH2n+2, not CnH2n.
  • Therefore, the correct answer is D, "Alkanes are represented by the general formula CnH2n".

MCQ 15:

Which of the following is not considered a physical property?





Topic: Physical and Chemical Properties

Correct Answer: D) Reactivity

Detailed Hint:
  • Physical properties are those that can be observed or measured without changing the identity of the substance. This includes properties such as melting point, boiling point, and solubility.
  • On the other hand, chemical properties describe how a substance interacts with other substances and include properties such as reactivity.
  • Hence, reactivity is a chemical property and not a physical one.
  • Therefore, the correct answer is D, "Reactivity".

MCQ 16:

Which of the following benzene derivatives undergoes electrophilic bromination more slowly than benzene itself?





Topic: Electrophilic Bromination of Benzene Derivatives

Correct Answer: D) C6H5 – NO2

Detailed Hint:
  • The rate of electrophilic bromination for benzene derivatives can vary depending on the substituent group attached to the benzene ring.
  • The substituent groups -CH3, -OH, and -NH2 are generally activating, increasing the rate of electrophilic bromination.
  • However, the -NO2 group is a deactivating group, which causes the benzene derivative to react more slowly in electrophilic bromination compared to benzene itself.
  • Therefore, the correct answer is D, "C6H5 – NO2".

MCQ 17:

Which of the following compounds exhibits the greatest ring strain?





Topic: Ring Strain in Cycloalkanes

Correct Answer: B) Cyclopropane

Detailed Hint:
  • Ring strain is a type of instability that exists when atoms in a cyclic molecule are forced out of their optimal spatial arrangements.
  • It is determined by factors such as bond angles, torsional strain, and non-bonded interactions.
  • In the case of cycloalkanes, cyclopropane exhibits the highest ring strain due to its small ring size and angular strain from bond angles being significantly less than the tetrahedral value.
  • Therefore, the correct answer is B, "Cyclopropane".

MCQ 18:

The preparation of benzene from acetylene could also be referred to as:





Topic: Conversion of Acetylene to Benzene

Correct Answer: B) Polymerization

Detailed Hint:
  • The conversion of acetylene to benzene involves the combination of three acetylene molecules.
  • This reaction occurs when acetylene is passed through a heated iron tube.
  • The process involves a type of polymerization known as trimerization, where three identical molecules combine.
  • Therefore, the correct term for this process is B, "Polymerization".

MCQ 19:

The combination of vinyl acetylene with HCl results in:





Topic: Reaction of Vinyl Acetylene with HCl

Correct Answer: C) Chloroprene

Detailed Hint:
  • Vinyl acetylene, a type of alkyne, can react with different substances to form various compounds.
  • When vinyl acetylene combines with hydrogen chloride (HCl), a hydrohalogenation reaction occurs.
  • This specific reaction results in the formation of a compound known as chloroprene.
  • Therefore, the correct answer is C, "Chloroprene".

MCQ 20:

Which elements make up hydrocarbons?





Topic: Composition of Hydrocarbons

Correct Answer: D) Both hydrogen and carbon

Detailed Hint:
  • Hydrocarbons are a class of organic compounds.
  • As their name suggests, they consist of entirely hydrogen and carbon atoms.
  • Oxygen is not a component of hydrocarbons, making option B incorrect.
  • Given the above, the correct answer is D, "Both hydrogen and carbon".

MCQ 21:

Which reaction process do primary alcohols undergo to form alkenes?





Topic: Reactions of Primary Alcohols

Correct Answer: A) Elimination

Detailed Hint:
  • Alcohols can undergo a variety of reactions, depending on the conditions and the type of alcohol.
  • Primary alcohols, when subjected to elimination or dehydration conditions, form alkenes.
  • Oxidation, reduction, and hydrolysis are not the processes through which primary alcohols form alkenes.
  • Therefore, the correct answer is A, "Elimination".

Question 22:

What is the name of the process associated with the acylation of benzene?





Topic: Reactions of Benzene

Correct Answer: A) Friedel craft reaction

Detailed Hint:
  • Benzene is a versatile organic compound that can engage in various reactions.
  • The process of acylation involves the introduction of an acyl group into a molecule.
  • In the context of benzene, this is commonly done through a reaction named after Charles Friedel and James Crafts.
  • Therefore, the correct answer is A, "Friedel craft reaction".

Question 23:

What is the bond angle deviation in cyclopropane?





Topic: Bond Angles in Cyclopropane

Correct Answer: A) 49.5°

Detailed Hint:
  • The bond angle in a molecule is the angle formed between three atoms across at least two bonds.
  • For cyclopropane, a three-membered cyclic hydrocarbon, the bond angles deviate significantly from the ideal 109.5° of a tetrahedral carbon atom.
  • The calculated deviation is obtained by subtracting the actual bond angle (60°) from the ideal (109.5°), resulting in a deviation of 49.5°.
  • Therefore, the correct answer is A, "49.5°".

Question 24:

What type of reaction is the halogenation of benzene in the presence of anhydrous AlCl3?





Topic: Halogenation of Benzene

Correct Answer: C) Electrophilic substitution

Detailed Hint:
  • Halogenation refers to a chemical reaction that incorporates a halogen into a molecule.
  • Benzene, being an aromatic compound, is rich in π electrons and can undergo various kinds of reactions.
  • When benzene is subjected to halogenation in the presence of anhydrous AlCl3, it undergoes an electrophilic substitution reaction, where a hydrogen atom is replaced by a halogen atom.
  • Therefore, the correct answer is C, "Electrophilic substitution".

Question 25:

Which compound is most resistant to a Friedel-Crafts reaction?





Topic: Resistance to Friedel-Crafts Reaction

Correct Answer: C) Nitrobenzene

Detailed Hint:
  • The Friedel-Crafts reaction is a type of electrophilic aromatic substitution reaction that involves the installation of an alkyl or acyl group onto an aromatic ring.
  • Some compounds are more resistant to these reactions depending on the electron density of their aromatic rings.
  • Nitrobenzene, with its electron-withdrawing nitro group, significantly reduces the electron density of its aromatic ring, making it less prone to Friedel-Crafts reactions.
  • Therefore, the correct answer is C, "Nitrobenzene".

Question 26:

What process converts a liquid hydrocarbon into a gaseous hydrocarbon?





Topic: Conversion of Hydrocarbons

Correct Answer: C) Cracking

Detailed Hint:
  • Hydrocarbons, compounds consisting solely of hydrogen and carbon, exist in various states depending on their molecular structure and size.
  • The conversion of a liquid hydrocarbon into a gaseous form involves breaking down larger molecules into smaller ones.
  • This process, known as cracking, typically requires high temperatures to facilitate the molecular breakdown.
  • Therefore, the correct answer is C, "Cracking".

Question 27:

Which of the following is not considered an organic addition reaction?





Topic: Organic Addition Reactions

Correct Answer: B) Dehydration

Detailed Hint:
  • Organic addition reactions are those where atoms or groups of atoms are added to a molecule without any other substance being eliminated.
  • Hydration, halogenation, and hydrohalogenation are all examples of such reactions.
  • Dehydration, on the other hand, involves the removal of a water molecule, making it an elimination reaction rather than an addition reaction.
  • Therefore, the correct answer is B, "Dehydration".

Question 28:

Which among the following is not classified as an organic compound?





Topic: Classification of Organic Compounds

Correct Answer: D) Electro compounds

Detailed Hint:
  • Organic compounds are primarily composed of carbon atoms bonded with hydrogen atoms and often also include other elements.
  • Carbonyl compounds, nitro compounds, and amides are all examples of classes of organic compounds.
  • Electro compounds, however, do not fit the established criteria for organic compounds and are thus not classified as such.
  • Therefore, the correct answer is D, "Electro compounds".

MCQs 29:

What is the product of the ozonolysis of benzene?





Topic: Ozonolysis of Benzene

Correct Answer: B) Glyoxal

Detailed Hint:
  • Ozonolysis is a process where ozone is used to cleave the unsaturated bonds in organic compounds, particularly alkenes and alkynes.
  • When benzene undergoes ozonolysis, the reaction results in the formation of a specific compound.
  • The product of this reaction is glyoxal, an organic compound with the formula OCHCHO.
  • Therefore, the correct answer is B, "Glyoxal".

MCQs 30:

Which type of hydrocarbon is characterized by all four valences of carbon being fully occupied?





Topic: Classification of Hydrocarbons

Correct Answer: C) Alkane

Detailed Hint:
  • Hydrocarbons are compounds consisting of hydrogen and carbon atoms.
  • The type of hydrocarbon is determined by the number of valences of carbon that are fully occupied.
  • In alkanes, all four valences of carbon are fully occupied, making them saturated hydrocarbons.
  • Therefore, the correct answer is C, "Alkane".

MCQs 31:

In which step does the homolysis of the Cl-Cl bond occur?





Topic: Homolysis in Chemical Reactions

Correct Answer: A) Initiation step

Detailed Hint:
  • Homolysis is a process where a compound is broken down into individual atoms, each with its own unpaired electron.
  • In certain chemical reactions, the Cl-Cl bond can undergo homolysis.
  • This occurs in the initiation step of the reaction where each Cl atom becomes very reactive.
  • Therefore, the correct answer is A, "Initiation step".

MCQs 32:

What is the resulting compound when alcohols undergo dehydration?





Topic: Dehydration of Alcohols

Correct Answer: A) Alkene

Detailed Hint:
  • Dehydration is a type of reaction where the removal of a water molecule from a substance occurs.
  • In the context of organic chemistry, alcohols can undergo dehydration.
  • This leads to the formation of alkenes, a type of hydrocarbon with a double bond.
  • Therefore, the correct answer is A, "Alkene".

MCQs 33:

Under high temperature and pressure conditions, what does an alkene transform into?





Topic: Transformation of Alkenes

Correct Answer: C) Polyalkane

Detailed Hint:
  • Alkenes are hydrocarbons that contain a carbon-carbon double bond.
  • When subjected to high temperature and high pressure, alkenes can undergo transformation.
  • Specifically, they undergo polymerization reaction to form polyalkanes, which are long chains of carbon atoms.
  • Therefore, the correct answer is C, "Polyalkane".

MCQs 34:

Which compound among the following explodes upon contact with oxygen?





Topic: Reactivity of Cycloalkanes

Correct Answer: A) Cyclopropane

Detailed Hint:
  • Cycloalkanes are types of hydrocarbon compounds which have carbon atoms arranged in a ring structure.
  • Not all cycloalkanes have the same reactivity with oxygen.
  • Cyclopropane, due to its strained ring structure, has a high reactivity and can explode on contact with oxygen.
  • Therefore, the correct answer is A, "Cyclopropane".

MCQs 35:

What is the geometrical shape of the benzene molecule?





Topic: Geometry of Benzene Molecule

Correct Answer: C) Hexagonal planar

Detailed Hint:
  • The geometry of a molecule refers to the three-dimensional arrangement of the atoms that constitute the molecule.
  • Benzene is categorized as an aromatic compound and these compounds typically have a planar structure.
  • Specifically, benzene has a hexagonal shape due to its six carbon atoms forming a ring.
  • Therefore, the correct answer is C, "Hexagonal planar".
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