Select the correct statement about the following reaction
`CH_3-undersetunderset(CH_3)(|)CH-CH_2-CH=CH_2overset(H_2//Ni)to(Y)overset(Cl_2//hv)to`Monochloro products

Options

A. The reactant (X) has four positional isomers ( includeing 'X' itself)
B. The hydrogenated product Y has three positional isomers
C. Four monochloro products are formed which are all positional isomers
D. Two alkyne can given Y on hydrogenation

Explanation

To solve the problem, we need to analyze the given reaction step by step.

### Step 1: Identify the Reactant
The reactant is given as:
\[ \text{CH}_3-\text{C}(\text{CH}_3)-\text{CH}_2-\text{CH}=\text{CH}_2 \]
This can be represented structurally as:
```
CH3
|
CH3 - C - CH2 - CH = CH2
```
This compound is a substituted alkene.

### Step 2: Hydrogenation Reaction
When the reactant is treated with hydrogen (H₂) in the presence of nickel (Ni), a hydrogenation reaction occurs. This means that the double bond in the alkene will be converted into a single bond, resulting in an alkane.

The product after hydrogenation (let's call it Y) will be:
\[ \text{CH}_3-\text{C}(\text{CH}_3)-\text{CH}_2-\text{CH}_2-\text{CH}_3 \]
This can be represented structurally as:
```
CH3
|
CH3 - C - CH2 - CH2 - CH3
```

### Step 3: Monochlorination Reaction
Next, the product Y undergoes monochlorination when treated with chlorine (Cl₂) under UV light (hv). Monochlorination means that one hydrogen atom in the alkane is replaced by a chlorine atom.

To determine the possible monochlorinated products, we need to identify all the unique positions where chlorine can be substituted.

### Step 4: Identify Monochlorinated Products
1. Chlorine at the terminal CH2 group:
\[ \text{CH}_3-\text{C}(\text{CH}_3)-\text{CH}_2-\text{CH}_2\text{Cl} \]

2. Chlorine at the second CH2 group:
\[ \text{CH}_3-\text{C}(\text{CH}_3)-\text{CH}\text{Cl}-\text{CH}_2-\text{CH}_3 \]

3. Chlorine at the third carbon (attached to the central carbon):
\[ \text{CH}_3-\text{C}(\text{CH}_3)-\text{C}\text{Cl}-\text{CH}_2-\text{CH}_3 \]

4. Chlorine at the second carbon (attached to the CH3 group):
\[ \text{CH}_3-\text{C}\text{Cl}-\text{CH}_2-\text{CH}_2-\text{CH}_3 \]

5. Chlorine at the terminal CH3 group:
\[ \text{CH}_3\text{Cl}-\text{C}(\text{CH}_3)-\text{CH}_2-\text{CH}_2-\text{CH}_3 \]

Thus, we can conclude that there are **five unique monochlorinated products**.

### Step 5: Analyze the Statements
Now, we need to analyze the statements provided in the question:

1. **Statement about positional isomers of reactant X**: The reactant has more than four positional isomers.
2. **Statement about the hydrogenated product Y**: Y has two positional isomers.
3. **Statement about monochlorinated products**: There are five monochlorinated products.
4. **Statement about alkynes forming Y**: Two alkynes can yield Y upon hydrogenation.

### Conclusion
Based on our analysis:
- The first statement is incorrect (it has more than four).
- The second statement is incorrect (it has two, not three).
- The third statement is correct (five monochlorinated products).
- The fourth statement is correct (two alkynes can yield Y).

Therefore, the correct answer is that the last two statements are correct.