Reduction of 2-butyne with sodium in liquid ammonia predominantly gives trans-2-butene.

Explanation:
- The reduction of 2-butyne with sodium in liquid ammonia is a classic example of a reaction known as dissolving metal reduction. This reaction involves the use of an alkali metal (such as sodium) dissolved in liquid ammonia as a strong reducing agent.
- In this reaction, the alkali metal (sodium) donates an electron to the triple bond of 2-butyne, resulting in the formation of a radical anion intermediate.
- The radical anion intermediate can then undergo various reactions, including elimination or hydrogenation, depending on the conditions.
- In the case of the reduction of 2-butyne with sodium in liquid ammonia, the radical anion intermediate undergoes hydrogenation, resulting in the formation of trans-2-butene as the major product.

The reasons why trans-2-butene is the major product in this reaction are as follows:

1. Steric hindrance:
- The presence of a bulky sodium metal in liquid ammonia creates steric hindrance, which favors the formation of the trans isomer.
- The bulky sodium metal prefers to approach the triple bond from the less hindered side, leading to the formation of the trans isomer.

2. Stability of the trans isomer:
- The trans isomer of 2-butene is more stable than the cis isomer due to the absence of steric interactions between the methyl groups.
- In the cis isomer, the methyl groups are in close proximity and experience steric repulsion, which destabilizes the molecule.

Therefore, the reduction of 2-butyne with sodium in liquid ammonia predominantly gives trans-2-butene as the major product. It is important to note that this reaction may also produce small amounts of other byproducts, such as cis-2-butene and n-butane, but trans-2-butene is the major product.