Step 1: Understanding the Concept:
The reactivity of a halogen atom in nucleophilic substitution depends on the strength and nature of the carbon-halogen (C-X) bond. Factors like resonance, hybridization, and steric hindrance play a crucial role.
Step 2: Detailed Explanation:
1. Chlorobenzene: The lone pair of electrons on the chlorine atom is in resonance with the $\pi$-electrons of the benzene ring. This gives the C-Cl bond a partial double bond character, making it very strong and difficult to break. Additionally, the carbon is $sp^{2}$ hybridized. It is the least reactive in this set.
2. Vinyl Chloride (\( \text{CH}_{2}=\text{CH-Cl} \)): Similar to chlorobenzene, resonance between the chlorine lone pair and the double bond creates partial double bond character. However, without the stabilization of an entire aromatic ring, it is slightly more reactive than chlorobenzene under specific conditions, though still very inert compared to alkyl halides.
3. Chloroethane (\( \text{CH}_{3}\text{CH}_{2}\text{Cl} \)): This is a simple primary alkyl halide. The carbon is $sp^{3}$ hybridized, and there is no resonance to stabilize the C-Cl bond. It undergoes nucleophilic substitution easily.
Thus, the ascending order (least to most reactive) is: Chlorobenzene < Vinyl chloride < Chloroethane.
Step 3: Final Answer:
The correct ascending order is chlorobenzene, vinyl chloride, chloroethane.