Important MCQs on Hydrocarbons with Explanation

Ans. (c) 2- Butanone.

Explanation: When 2- Butyne is treated with dil. H₂SO₄/HgSO₄, 2- Butanone is formed. It is an example of Alkyne Hydration. The product formation takes place as per Markovnikov’s Rule. It states that an electrophile (electron-rich atom) tends to bond easily and more effectively with the carbon atom which contains a lesser number of hydrogen atoms.

Ans. (d) NHCOCH₃

Explanation: The electron density affects the ortho, para, and meta positioning of the non-hydrogen substituents. Basically, the ortho and para groups are electron donating groups. The electron density on the C=O in NHCOCH₃ is less as compared to its other counterparts. The group also possesses a partial positive charge. COOH and COCH₃, along with CN, are meta-directing.

Ans. (a) Pd/H₂

Explanation: The conversion of Butene to Butane depicts the addition of hydrogen and the formation of a saturated hydrocarbon. Here, an alkene is converted to alkane. Thus, the above reaction is a hydrogenation reaction. The reaction is carried out in the presence of catalysts like Palladium, Platinum or Nickel.

Ans. (d) Ethyne

Explanation: The reaction is as follows: 

Ans. (c) HC ≡ CH

Explanation: When Bromine in presence of Carbon tetrachloride, is added to acetylene or ethyne, the product formed is a Bromo-derivative of alkene. In this case, the product formed is dibromoethane.

Read More: Acetone

Ans. (a) CH3= CH₂ CH = C(CH₃)₂

Explanation: The products for this reaction are propanal (CH₃CH₂CHO) and acetone (CH₃COCH₃). Since the reaction involves ozonolysis, the double bond after three carbon atoms must lead to cleavage and formation of carbonyl compounds and an isopropyl group. The presence of an isopropyl group, a five-carbon base chain and a double bond after three carbon atoms constitute the formation of the two carbonyl compounds.

Ans. (b) Tert-butyl benzene

Explanation: Benzene on reaction with isobutene in the presence of sulphuric acid, gives tert-butyl benzene as a product. The reaction here that the reactants undergo is an electrophilic aromatic substitution reaction. Tert-butyl is also called cumene. The reaction implies the acidification of isobutene. The intermediate tertiary carbocation formed reacts with benzene to give cumene as the final product.

Ans. (d) sp² – sp³

Explanation: Hybridization is the process of combining two different orbitals to form a new type of hybridized orbital. The compound shows sp² – sp³ hybridization. C₂ consists of a double bond giving away 3 sigma bonds. Hence sp² hybridization. C₃ on the other hand consists of 4 single bonds representing sp³ hybridization.

Ans. (b) One sigma and two pi bonds

Explanation: The given compound is Calcium carbide. The compound consists of 2 anions (C) and a cation (Ca). The ionic structure of Calcium carbide consists of the triple bond between the carbon atoms and a single bond between each calcium and carbon atom. 

Ans. (a) NaOH

Explanation: Acetylene is a weak acid and NaOH is a strong base. The formation of a strong acid is impossible in an acid-base neutralization reaction when the reactant is a weak acid. Along with a strong acid, the products formed will be water and stronger base salt. Hence, Acetylene does not react with Sodium hydroxide.

Ans. (c) 5

Explanation: Isomerism is a phenomenon wherein one compound has the same chemical formula yet different chemical structures. There is a difference in the arrangement of atoms but the chemical formula remains the same. The 5 isomers of hexane are- hexane, 2- methylpentane, 2,2- dimethylbutane, 3- methylpentane, 2,3- dimethylbutane.

Ans. (c) i > iv > ii > iii

Explanation: The bond length in alkanes is more than that of the alkenes. Alkenes feature one sigma bond and one pi bond. Although benzene indicates one sigma and one pi bond, there is delocalization of bonds which leads to the density distribution among the rings. Hence, the bond seems shorter. Conclusively, the increasing order of the bond length is as follows: Ethane>Benzene>Ethene>Acetylene

Ans. (c) SO₃

Explanation: Sulphonation of benzene constitutes an electrophilic substitution reaction that takes place in the presence of sulphuric acid. It is a reversible reaction. It is used in the production of benzene sulphonic acid. The steps involved in sulphonation are as follows: Electrophile formation, the attack of benzene on electrophile, followed by the removal of hydrogen by oxygen located on sulfur trioxide.

Ans. (d) Isopropyl chloride

Explanation: Friedel-Crafts reaction forms carbocations in the presence of chlorobenzene, bromobenzene, chloroethane, etc. It is an organic coupling reaction that involves electrophilic aromatic substitution which is used for the attachment of substituents to aromatic rings. The lone pair of electrons present on the halogens are delocalized with pi bonds to attain double bond character. Hence, isopropyl chloride can be used as a halide component for a Friedel-Craft reaction.