Free Alkynes MCQs with Answers

• A. one sigma and two pi bonds between the carbon atoms, with sp hybridisation
• B. two sigma bonds between the carbon atoms
• C. only sigma bonds
• D. three pi bonds between the carbon atoms

Explanation: A triple bond is always one sigma bond plus two pi bonds, formed from two unhybridised p orbitals on each sp hybridised carbon, and the…

• A. calcium carbonate
• B. calcium oxide
• C. calcium hydroxide
• D. calcium carbide

Explanation: Calcium carbide reacts vigorously with water to give ethyne and calcium hydroxide, which was once used in carbide lamps and is still the…

• A. the triple bond adds silver
• B. the hydrogen attached to the triply bonded carbon is weakly acidic and is replaced by silver
• C. silver catalyses polymerisation
• D. alkynes are strong bases

Explanation: The sp hybridised carbon holds its bonding electrons closer, so the attached hydrogen is slightly acidic and can be replaced by a metal to…

• A. Terminal carbon atoms are sp hybridized
• B. Terminal carbon atoms are sp2 hybridized
• C. Terminal carbon atoms are sp3 hybridized
• D. Terminal carbon atoms show hydrogen bonding

Explanation: An sp hybrid orbital has 50 per cent s character, so it holds the bonding electrons closer to the carbon nucleus and the attached hydrogen…

• A. CH3-CH2-CCH (1-Butyne)
• B. CH3-CCH(1-Propyne)
• C. CH3-CH2-CH2CCH(1-Pentyne)
• D. CH2=CH2

Explanation: Terminal alkynes such as 1-butyne, 1-propyne and 1-pentyne contain an acidic terminal hydrogen and form red copper acetylide precipitates…

• A. Ethyne
• B. Ethene
• C. Ethane
• D. Benzene

Explanation: Ethyne has a terminal C-H bond attached to an sp-hybridised carbon. Its high s-character makes this hydrogen relatively acidic compared…

• A. Glycol
• B. Glyoxal then formic acid
• C. Formaldehyde
• D. None

Explanation: Ozonolysis of acetylene first forms glyoxal, OHC-CHO, and further oxidation converts the aldehyde groups to formic acid.

• A. CH3CH2CHO + CH3CHO
• B. CH3CH2CHO + CH3COOH
• C. CH3CH2COOH + CH3COOH
• D. CH3COOH + CO2

Explanation: In oxidative ozonolysis without zinc, 2-pentyne, CH3-C≡C-CH2CH3, is cleaved at the triple bond and both resulting fragments are oxidised…

• A. Acetone
• B. Acetaldehyde
• C. Acetic acid
• D. Ethyl alcohol

Explanation: Water adds across ethyne in the presence of HgSO4 and H2SO4 to form an unstable enol, CH2=CHOH.

• A. Methane
• B. Ethane
• C. Acetylene
• D. Ethene

Explanation: Acetylene burns with oxygen to produce an extremely hot flame, so the oxyacetylene flame is used for welding and cutting metals.

• A. Bromine water
• B. Bayer's reagent
• C. Fehling solution
• D. Ammonical silver nitrate

Explanation: A triple bond in a terminal alkyne such as propyne, C3H4, is indicated by ammoniacal silver nitrate, which forms a precipitate of silver…

• A. White precipitate with AgNO3 and red precipitate with Cu2Cl2
• B. White precipitate with Cu2Cl2 and red precipitate with AgNO3
• C. White precipitate with both the reagents
• D. Red precipitate with both the reagents

Explanation: Terminal acetylene forms white silver acetylide with ammoniacal AgNO3 and red copper acetylide with ammoniacal cuprous chloride, written…

• A. Alkane
• B. Alkene
• C. Alkyne
• D. All have same

Explanation: A terminal alkyne is more acidic because its conjugate base places the negative charge on an sp-hybridised carbon, which has greater…

• A. CnH2n + 2
• B. CnH2n - 2
• C. CnH2n
• D. CnH2n + 2

Explanation: An open-chain alkyne has the general formula CnH2n-2 because it contains one triple bond, which represents two degrees of unsaturation.

• A. ethene
• B. ethyne
• C. ethyl halide
• D. all of the above are possible

Explanation: Complete dehalogenation of a tetrahaloethane removes four halogen atoms from the two-carbon framework, creating two pi bonds and forming…

• A. propyne
• B. 1-butyne
• C. ethyne
• D. all of the above

Explanation: Propyne, 1-butyne and ethyne are all terminal alkynes, so each has a hydrogen attached to a triple-bonded carbon and can show weak acidic…

• A. angular
• B. trigonal
• C. linear
• D. trigonal planar

Explanation: Ethyne, C2H2, contains a carbon-carbon triple bond. Each carbon is sp-hybridized, and sp orbitals are arranged 180° apart, so the molecule…

• A. Diviny1 acetylene
• B. Ethylidine dichloride
• C. Chloroprene
• D. 1 - 3 - 3 - trichloro butane

Explanation: Addition of one molecule of HCl to vinyl acetylene, CH2=CH-C≡CH, gives 2-chloro-1,3-butadiene, commonly called chloroprene.

• A. Acetaldehyde
• B. Propanal
• C. 2-Butanol
• D. Butanone

Explanation: The acid hydrolysis of an alkyne, such as CH3-C≡C-CH3, in the presence of a mercury(II) sulfate (HgSO4) catalyst proceeds through a…

• A. 1-Butyne
• B. 2-Butyne
• C. 2-Pentyne
• D. 3-Hexyne

Explanation: 1-Butyne has a terminal triple bond, so it can exhibit acidic properties.