Which one of the following pairs of reaction types included in the reaction sequence below
`CH_(3)CH = CHCH_(3) + HI ("in" CH_(3)COOH) rarr CH_(3)CH_(2)CHICH_(3)`
`CH_(3)CH_(2)CHICH_(3) + NaOH(aq) rarr CH_(3)CH_(2)CH(OH)CH_(3)`

Options

A. Electrophilic addition and electrophilic substitution
B. Electrophilic addition and nucleophilic substitution
C. Nucleophilic addition and electrophilic substitution
D. Nucleophilic addition and free radical substitution

Answer

To analyze the reaction sequence provided, we need to identify the types of reactions occurring in each step.

### Step 1: Analyzing the First Reaction
**Reaction:**
\[ \text{CH}_3\text{CH}=\text{CHCH}_3 + \text{HI} \xrightarrow{\text{in } \text{CH}_3\text{COOH}} \text{CH}_3\text{CH}_2\text{CHI}\text{CH}_3 \]

1. **Identify the Reactants:**
- The reactant is an alkene (CH3-CH=CH-CH3) and hydrogen iodide (HI).

2. **Type of Reaction:**
- The reaction involves the addition of HI to the double bond of the alkene.
- This is an **Electrophilic Addition Reaction** because the alkene acts as a nucleophile and the HI provides the electrophile (H+).

3. **Mechanism:**
- The double bond in the alkene attacks the H+ from HI, forming a carbocation intermediate. The iodide ion (I-) then attacks the carbocation, resulting in the formation of the product (CH3-CH2-CHI-CH3).

### Step 2: Analyzing the Second Reaction
**Reaction:**
\[ \text{CH}_3\text{CH}_2\text{CHI}\text{CH}_3 + \text{NaOH(aq)} \rightarrow \text{CH}_3\text{CH}_2\text{CH(OH)}\text{CH}_3 \]

1. **Identify the Reactants:**
- The reactant is CH3-CH2-CHI-CH3 and sodium hydroxide (NaOH).

2. **Type of Reaction:**
- The reaction involves the substitution of the iodine atom (leaving group) with a hydroxyl group (OH).
- This is a **Nucleophilic Substitution Reaction** because the hydroxide ion (OH-) acts as a nucleophile that replaces the iodide ion (I-).

3. **Mechanism:**
- The OH- ion attacks the carbon atom bonded to the iodine, leading to the displacement of the iodide ion and forming the alcohol (CH3-CH2-CH(OH)-CH3).

### Conclusion
The two types of reactions identified in the sequence are:
1. **Electrophilic Addition** (first reaction)
2. **Nucleophilic Substitution** (second reaction)

### Final Answer
The correct answer is:
- **Electrophilic Addition** and **Nucleophilic Substitution**.

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