Answer:
Addition of hydrogen in unsaturated hydrocarbons is known as Hydrogenation.
Major product that is formed when 2-butyne is treated with an excess of hydrogen gas and a platinum catalyst is an alkane of four carbon atom known as butane.
Here hydrogen gas is in excess, first but-2-ene will form from the but-2-yne then butane will form from the but-2ene.
1) [tex]CH_3-CH\equiv CH-CH_3\overset{H_2/Pt}\rightarrow CH_3-CH=CH-CH_3[/tex]
2) [tex]CH_3-CH=CH-CH_3\overset{H_2/Pt}\rightarrow CH_3-CH_2-CH_2-CH_3[/tex]
As shown in the image attached.