A set of compounds in which the reactivity of halogen atoms in the ascending order is

Chlorobenzene, vinyl chloride, chloroethane

The correct answer is option 2. chlorobenzene, vinyl chloride, chloroethane.

Let us explain why the reactivity of halogen atoms varies in chloroethane, chlorobenzene, and vinyl chloride, leading to the given order.

Factors Affecting Reactivity of Halogen Atoms:

Bond Strength: Stronger carbon-halogen bonds are harder to break, leading to lower reactivity.

Hybridization: The hybridization state of the carbon atom affects the bond strength. Generally, sp² hybridized carbons form stronger bonds with halogens compared to sp³ hybridized carbons.

Resonance and Inductive Effects: Resonance can stabilize the carbon-halogen bond, reducing reactivity. Inductive effects from adjacent groups also play a role.

Analysis of Each Compound:

Chloroethane \((C_2H_5Cl)\)

Chloroethane consists of an ethyl group \((C_2H_5)\) bonded to a chlorine atom. The carbon bonded to chlorine is \(sp^3\) hybridized. The C-Cl bond in chloroethane is a single bond (σ-bond), which is relatively weak compared to bonds involving sp² hybridized carbons or those stabilized by resonance. Due to the weaker \(C-Cl\) bond, chloroethane has the highest reactivity among the three compounds.

Chlorobenzene \((C_6H_5Cl)\)

Chlorobenzene consists of a benzene ring (\(C_6H_5)\) bonded to a chlorine atom. The carbon bonded to chlorine is \(sp^2)\) hybridized. The benzene ring provides resonance stabilization. The lone pairs on chlorine can participate in resonance with the π-electrons of the benzene ring, which delocalizes the electron density and strengthens the \(C-Cl\)bond. The \(C-Cl\) bond in chlorobenzene is strengthened by resonance and the\( sp^2\) hybridization. Due to the strong resonance stabilization and the strong \(C-Cl\) bond, chlorobenzene has the lowest reactivity among the three compounds.

Vinyl Chloride \((CH_2=CHCl)\)

Vinyl chloride consists of a vinyl group \(CH_2=CH)\) bonded to a chlorine atom. The carbon bonded to chlorine is \(sp^2\) hybridized. The \(C-Cl\) bond in vinyl chloride is stronger than in chloroethane due to the \(sp^2\) hybridization but weaker than in chlorobenzene because there is no resonance stabilization like in chlorobenzene.  The \(C-Cl\) bond in vinyl chloride is stronger than in chloroethane but weaker than in chlorobenzene, giving it intermediate reactivity.

Conclusion:
The reactivity of the halogen atoms in these compounds is influenced by the bond strength and stabilization mechanisms such as resonance and hybridization:

Chlorobenzene has the least reactive halogen due to resonance stabilization in the aromatic ring. Vinyl Chloride has moderate reactivity due to the \(sp^2\) hybridization of the carbon but lacks the resonance stabilization found in chlorobenzene. Chloroethane is the most reactive because the \(C-Cl\) bond is the weakest, being a simple σ-bond with \(sp^3\) hybridization and no resonance stabilization.

Thus, the correct ascending order of reactivity of halogen atoms is: Chlorobenzene < Vinyl Chloride < Chloroethane

This matches the option: Chlorobenzene, vinyl chloride, chloroethane.