Which of the following reactions is shown by alkynes

Options

A. Addition
B. Substitution
C. Polymerization
D. All of these

Explanation

To determine which reactions are shown by alkynes, we can analyze the types of reactions that alkynes typically undergo. Let's break it down step by step.

### Step 1: Understanding Alkynes
Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond (C≡C). The simplest alkyne is ethyne (C2H2).

### Step 2: Addition Reactions
Alkynes commonly undergo addition reactions. This is because the triple bond is reactive and can add atoms or groups across the triple bond. For example, ethyne can react with hydrogen halides (HX) to form haloalkenes.

**Example Reaction:**
\[ \text{HC≡CH} + \text{HCl} \rightarrow \text{HC=CHCl} \]

### Step 3: Substitution Reactions
Alkynes can also participate in substitution reactions. For instance, when treated with a strong base like sodium amide (NaNH2), they can form an alkyne salt, which can then act as a nucleophile and react with alkyl halides to form substituted products.

**Example Reaction:**
\[ \text{RC≡C}^- + \text{R'X} \rightarrow \text{RC≡CR'} + \text{X}^- \]

### Step 4: Polymerization Reactions
Alkynes can undergo polymerization, where multiple alkyne molecules combine to form larger structures. For example, three moles of ethyne can polymerize in the presence of a catalyst to form benzene.

**Example Reaction:**
\[ 3 \text{C2H2} \xrightarrow{\text{catalyst}} \text{C6H6} \]

### Conclusion
Based on the analysis above, alkynes can show:
1. Addition reactions
2. Substitution reactions
3. Polymerization reactions

Thus, the correct answer is that alkynes can exhibit all of these reactions.

### Final Answer
Alkynes show addition reactions, substitution reactions, and polymerization reactions.

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