This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Alkynes”.
1. Alkynes are more reactive than alkenes.
a) False
b) True
View Answer
Explanation: Alkynes are not as reactive when compared with the alkenes and the alkanes as they even more unsaturated when compared with them.
2. Select the incorrect statement.
a) The addition reactions occur more frequently in the alkenes than the alkynes
b) The pi system of the alkynes gets weakened when they lose the pi atoms
c) Alkynes readily undergo oligomerization
d) Alkynes do not undergo polymerization
View Answer
Explanation: Alkynes readily undergo polymerization and form polymers such as polyacetylenes.
3. Select the incorrect statement regarding terminal alkynes.
a) Methylacetylene is an example of terminal alkynes
b) Terminal alkynes are more acidic when compared with alkenes
c) Terminal alkynes are not as acidic as alkanes
d) These have a replaceable acidic hydrogen atom
View Answer
Explanation: Terminal alkynes are very much acidic than both alkenes and alkanes as they have a high pKa value.
4. The major alkyne, acetylene compound is produced by which among the following application on natural gas?
a) Hydrogenation
b) Partial oxidation
c) Cracking
d) Hydrohalogenation
View Answer
Explanation: A huge quantity of acetylene is produced by partial oxidation of the natural gas.
5. Majority of the alkynes are not prepared from/by ___________
a) Condensation
b) Acetylene
c) Dehydrohalogenation
d) Hydrogenation
View Answer
Explanation: Often, alkynes are obtained from the acetylene through the condensation process and sometimes by dehydrohalogenation.
6. Alkynes cannot be prepared from ___________
a) Ketones
b) Alcohols
c) Aldehydes
d) Other alkynes
View Answer
Explanation: Only the aldehydes, ketones, and few other alkynes can give rise to a new alkyne compound.
7. The transformation into carboxylic acids of the alkynes takes place with the help of which among the following reagents?
a) Potassium chlorate
b) Potassium permanganate
c) Potassium dichromate
d) Potassium chloride
View Answer
Explanation: The cycloaddition of the alkynes leads to the oxidative cleavage among them and hence it results in the formation of carboxylic acids.
8. Identify the incorrect statement.
a) Alkynes exists in gaseous state
b) They are soluble in water
c) They are soluble in organic solvents
d) Alkynes have a very good boiling point
View Answer
Explanation: Alkyne molecules being non-polar, they do not dissolve in polar solvents like water.
9. Which among the following alkynes is used as a rocket fuel?
a) Ethyne
b) Propyne
c) But-1-yne
d) Pent-1-yne
View Answer
Explanation: Propyne has many advantages and it is not as hazardous as compared to the other fuels, so they are used in rocket fuels.
10. Which among the following product is formed when ethyne undergoes hydrogenation?
a) Formaldehyde
b) Formic acid
c) Acetaldehyde
d) Acetic acid
View Answer
Explanation: When ethyne undergoes hydrogenation in the presence of sulphuric acid, it forms ethanal.
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