This set of Class 11 Chemistry Chapter 13 Multiple Choice Questions & Answers (MCQs) focuses on “Hydrocarbons – Alkenes”.
1. Alkenes are not called olefins.
Explanation: Alkenes are unsaturated noncyclic hydrocarbons which have sp2 hybridization with 120-degree bond angle. They are called olefins which mean oil forming and it indicates they are highly reactive nature alkynes general formula is CnH2n.
2. Ethene is prepared from chloroethane this is an example of a reaction __________
a) from alkynes
b) removal of vicinal dihalides
c) acidic dehydrogenation
Explanation: When chloroethane is heated in the presence of alcoholic potassium Hydroxide, a beta-elimination product is formed, that is ethane, hydrogen, and chlorine are removed which is dehydrohalogenation (the halogen can be either chlorine or bromine or iodine).
3. Alkene __________ in the physical properties of alkanes.
a) there is no comparison
b) differ completely
c) differ in a few aspects
d) same as
Explanation: Alkenes as a class resemble alkanes in physical properties, except in types of isomerism and difference in polar nature. The first three of the series are gases, the next 14 are liquid and the higher members are solids they show a regular increase in boiling point with an increase in size.
4. Alkenes show __________ isomerism.
a) only structural
b) only geometrical
c) both geometrical and structural
d) neither geometrical nor structural
Explanation: Alkynes show both structural isomerism as well as geometrical isomerism, structural isomerism exhibited by alkenes are chain isomerism and position isomerism, while alkenes also exhibit stereoisomerism as geometrical cis-trans isomerism.
5. Addition reaction of hydrogen Bromide to the unsymmetrical alkene follows __________
a) anti markovnikov’s rule
b) markovnikov’s rule
c) kharish effect
d) peroxide effect
Explanation: According to markovnikov’s rule the negative part of the addendum which means adding molecule, gets attached to that carbon atom which possesses less number of hydrogen atoms, it’s the opposite of anti markovnikov’s rule.
6. What is kharash effect?
b) Peroxide effect
c) Markovnikov’s rule
d) Addition of hydrogen
Explanation: Anti markownikoff rule is also known as peroxide effect and kharash effect; in the presence of organic peroxide, the addition of only hydrogen Bromide molecule on unsymmetrical alkene, takes place contrary to the markovnikov rule.
7. Which of the following is a Bayer’s reagent?
a) The neutral solution of HCL
b) An alcoholic solution of sodium carbonate
c) An acidic solution of potassium hydroxide
d) An aqueous solution of potassium permanganate
Explanation: The dilute aqueous solution of potassium permanganate is known as Bayer’s reagent. Alkenes decolorize Bayer’s reagent and it is used as a test for unsaturation in alkenes. It is a powerful oxidant as well as a syn-reaction occurs.
8. Which of the following compound is more acidic?
d) All of them are equally acidic
Explanation: The acidic behavior depends upon the hybridization of the molecule as we know that alkane has sp3 hybridization, alkane has sp2 hybridization and alkynes has sp hybridization, due to the higher percentage of s-character, alkyne becomes highly acidic when compared with alkene and alkane.
9. What is the intermediate conformation between eclipsed and staggered?
Explanation: The intermediate conformation between eclipsed and staggered is known as skew and gauche formations. The eclipsed form is least stable but the staggered form is the most stable due to the greater distance between the bond pairs or lesser torsional strain.
10. Which of the following statement is true regarding the reactivity order in order to form alkyl halides?
a) Hydrogen iodide is less than that of hydrogen Bromide
b) Hydrogen Bromide is less than that of HCL
c) HCL is greater than that of hydrogen iodide
d) Hydrogen Bromide is less than that of hydrogen iodide
Explanation: In chemical properties of alkenes, HCL, hydrogen Bromide and hydrogen iodide are added to alkenes to form alkyl halides as per their reactivity order that is; hydrogen iodide’s reactivity is greater than that of hydrogen Bromide and it is greater than that of HCL.
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