Identify (Z) in the following reaction series,
`C_2H_5Ioverset("Alcoholic")underset("KOH")rarr(X)overset(Br_2)rarr (Y)overset(KCN)rarr (Z)`

Options

A. `CH_3-CH_2-CN`
B. `underset(CN)underset(|)CH_2-underset(CN)underset(|)CH_2`
C. `underset(Br)underset(|)CH_2-underset(CN)underset(|)CH_2`
D. `underset(Br)underset(|)CH=underset(CN)underset(|)"CH"`

Explanation

To identify compound (Z) in the reaction series provided, we will analyze each step of the reaction:

### Step 1: Reaction of C2H5I with Alcoholic KOH
- The starting compound is **C2H5I** (ethyl iodide).
- When ethyl iodide reacts with alcoholic KOH, it undergoes **beta elimination** (dehydrohalogenation), which involves the removal of HI (hydrogen iodide).
- The reaction can be represented as:
\[ C_2H_5I + KOH \rightarrow C_2H4 + HI \]
- The product formed (X) is **ethene (C2H4)**.

### Step 2: Reaction of Ethene with Br2
- The next step involves the reaction of ethene with bromine (Br2).
- Ethene undergoes an **electrophilic addition** reaction with bromine, resulting in the formation of **1,2-dibromoethane** (Y).
- The reaction can be represented as:
\[ C_2H4 + Br_2 \rightarrow C_2H4Br_2 \]
- The product formed (Y) is **1,2-dibromoethane** (C2H4Br2).

### Step 3: Reaction of 1,2-Dibromoethane with KCN
- Finally, 1,2-dibromoethane reacts with potassium cyanide (KCN).
- In this reaction, the bromine atoms are substituted by cyanide groups (–CN), as cyanide is a good nucleophile.
- The reaction can be represented as:
\[ C_2H4Br_2 + 2 KCN \rightarrow C_2H4(CN)_2 + 2 KBr \]
- The product formed (Z) is **1,2-dicyanoethane** (C2H4(CN)2).

### Conclusion
- Therefore, the final compound (Z) is **1,2-dicyanoethane**.

### Summary of Compounds:
- **X**: Ethene (C2H4)
- **Y**: 1,2-Dibromoethane (C2H4Br2)
- **Z**: 1,2-Dicyanoethane (C2H4(CN)2)