What is X in the following reaction?

What is X in the following reaction?

1. $\mathrm{H}_3 \mathrm{C}-\mathrm{CH}_2-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_2-\mathrm{CH}_2 \mathrm{Br}$
2. 
   
3. 
   
4. 
   

Asked in: AP EAMCET 2024 (20 May Shift 2)

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