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The acidity of acetylene or terminal alkynes can be justified using the molecular orbital theory, which states that the C–H bond in acetylene arises from an sp-hybridized carbon atom. Which of the following statements support this explanation?

1. The electrons in an sp orbital are closer to the nucleus compared to those in a p orbital.
2. A bond with higher s-character has electrons that are held closer to the nucleus.
3. Due to the high s-character (50%) in the C–H bond of alkynes, the electrons in this bond are more tightly bound to the carbon nucleus, making the sp orbital more electronegative than sp2 and sp3 orbitals, which allows the hydrogen atom in ≡C–H to be easily removed as a proton.
4. All of the above statements are correct.

Correct answer: All of the above statements are correct.

Solution

The acidity of acetylene is due to the high s-character (50%) of the sp-hybridized carbon, which makes the C-H bond electrons closer to the nucleus and the bond more polarizable, allowing easier proton removal. All statements collectively explain this phenomenon.

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