Addition of water to alkynes occurs in acidic medium and in the presence of Hg2+ ions as a catalyst. Which of the following products will be formed on addition of water to but-1-yne under these conditions?

1.
2.
3.
4.

Hint: Follows oxymercuration-demercuration reaction, 

This reaction is an example of an Oxymercuration - Demercuration reaction in which an alkyne is converted into ketone in the presence Hg2+ ions as a catalyst. When But-1-yne on reaction with water in presence of Hg2+ ions as a catalyst then butan-2-one is obtained as the product.

The reaction is as follows: