When 2-butyne is treated with `H_2//Pd - BaSO_4`, the product formed will be :

Options

A. cis-2-butene
B. trans-2-butene
C. 1-butene
D. 2-hydroxy butane

Explanation

To solve the question of what product is formed when 2-butyne is treated with `H_2 // Pd - BaSO_4`, we can follow these steps:

### Step 1: Understand the Structure of 2-Butyne
2-butyne has the structure:
\[ \text{CH}_3 - \text{C} \equiv \text{C} - \text{CH}_3 \]
This means there is a triple bond between the second and third carbon atoms.

### Step 2: Identify the Reaction Conditions
The reaction involves the use of hydrogen gas (`H_2`) in the presence of a palladium catalyst supported on barium sulfate (`Pd - BaSO_4`). This setup is typically used for the partial hydrogenation of alkynes.

### Step 3: Determine the Type of Addition
The reaction with `H_2 // Pd - BaSO_4` leads to a syn addition. This means that both hydrogen atoms will add to the same side of the double bond formed during the reaction.

### Step 4: Predict the Product
When 2-butyne undergoes syn addition of hydrogen, it will convert to a cis-alkene. The product will be:
\[ \text{Cis-2-butene} \]
The structure of cis-2-butene can be represented as:
\[ \text{CH}_3 - \text{C} = \text{C} - \text{CH}_3 \]
with both methyl groups (CH₃) on the same side of the double bond.

### Step 5: Compare with Given Options
The options provided were:
1. 2-butane
2. Trans-2-butene
3. 1-butene
4. 2-hydroxybutane

From our prediction, the product formed is cis-2-butene, which is not listed among the options. However, since the question asks for the product of the reaction, we can conclude that the closest option is 2-butene, which is the correct answer.

### Final Answer
The product formed when 2-butyne is treated with `H_2 // Pd - BaSO_4` is **cis-2-butene** (or simply 2-butene).

---