Identify Z in the following reaction sequence
`C_(2)H_(5)Ioverset(alc.KOH)toXoverset(Br_(2))toYoverset(KCN)toZ`

Options

A. `Br-CH_(2)-CH_(2)-CN`
B. `CH_(3)CH_(2)-CN`
C. `CN-CH_(2)-CH_(2)-CN`
D. BrCH = CHCN

Explanation

To identify compound Z in the given reaction sequence, we will analyze each step carefully:

### Step 1: Identify X from C2H5I using alcoholic KOH
1. **Starting Compound**: Ethyl iodide (C2H5I).
2. **Reagent**: Alcoholic KOH is used for dehydrohalogenation.
3. **Reaction**: The alcoholic KOH removes the iodine (I) and a hydrogen (H) from the ethyl iodide, resulting in the formation of an alkene.
4. **Product**: The product formed is ethene (C2H4).
- **X = C2H4 (Ethene)**

### Step 2: Identify Y from X using Br2
1. **Starting Compound**: Ethene (C2H4).
2. **Reagent**: Bromine (Br2) is used for the addition reaction across the double bond.
3. **Reaction**: The Br2 adds across the double bond of ethene, resulting in the formation of 1,2-dibromoethane.
4. **Product**: The product formed is 1,2-dibromoethane (C2H4Br2).
- **Y = C2H4Br2 (1,2-Dibromoethane)**

### Step 3: Identify Z from Y using KCN
1. **Starting Compound**: 1,2-dibromoethane (C2H4Br2).
2. **Reagent**: Potassium cyanide (KCN) is used in this step.
3. **Reaction**: KCN acts as a nucleophile, where the bromine (Br) atoms are good leaving groups. The cyanide ion (CN-) replaces the bromine atoms.
4. **Product**: The product formed is 1,2-ethanediamine (C2H4(CN)2), which can also be represented as 1,2-dicyanoethane.
- **Z = C2H4(CN)2 (1,2-Dicyanoethane)**

### Final Answer
Thus, the compound Z is **1,2-dicyanoethane (C2H4(CN)2)**.

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