When but-2-yne is hydrated with conc. `H_2 SO_4` in the presence of `Hg So_4` it gives .......

Explanation

To solve the problem of what product is formed when but-2-yne is hydrated with concentrated H₂SO₄ in the presence of HgSO₄, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants are but-2-yne (C₄H₆) and the reagents, which are concentrated sulfuric acid (H₂SO₄) and mercuric sulfate (HgSO₄).

2. **Formation of a Carbocation**: When but-2-yne reacts with H₂SO₄, the alkyne undergoes protonation to form a carbocation. The triple bond in but-2-yne is electron-rich and will attack the H⁺ from H₂SO₄. This results in the formation of a non-classical carbocation.

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