Identify 'Z' in the following series of reaction

Identify 'Z' in the following series of reaction
  1. Butan-1-ol
  2. 2-chlorobutane
  3. Butan-2-ol
  4. But-2-ene

Asked in: MHT CET 2020 (12 Oct Shift 1)

Practice more Halogen Derivatives questions on Aicharya