Identify monomer by reversing addition polymerization

Steps:

• Examine the repeat unit structure in the polymer section to identify the carbon chain and substituents.
• Locate the connection between repeat units, which formed by breaking the monomer's double bond.
• Reconstruct the monomer by adding a double bond between the carbons that linked during polymerization.
• Match the resulting structure to the given options, confirming the chloro and methyl positions.

Why B is correct:

• 2-Chloro-3-methylbut-2-ene is an alkene that undergoes addition polymerization, opening the C=C bond to form the observed repeat unit with chlorine intact.

Why the others are wrong:

• A: Alkane lacks a double bond, cannot form addition polymer.
• C: Alkyne would produce a different repeat unit via triple bond addition, not matching the structure.
• D: Dihaloalkane suggests substitution polymerization, not addition, and has extra chlorines.

Final answer: B