Explain the preparation of alkene from alkyl halide via dehydrohalogenation in detail.

(N/A) Preparation: Alkyl halides $(RX)$ undergo $\beta$-elimination when heated with alcoholic potassium hydroxide (potassium hydroxide dissolved in ethanol).
Reaction Mechanism: In this reaction,a hydrogen atom is removed from the $\beta$-carbon and a halogen atom is removed from the $\alpha$-carbon,resulting in the release of $HX$ and the formation of an alkene. This process is known as dehydrohalogenation or $\beta$-elimination.
General Reaction: $R-CH_2-CH_2-X + KOH (\text{alc.}) \xrightarrow{\Delta} R-CH=CH_2 + KX + H_2O$.
Factors affecting the rate of reaction:
$(i)$ Nature of the halogen: The rate follows the order $I > Br > Cl$.
$(ii)$ Nature of the alkyl group: The rate follows the order $3^{\circ} > 2^{\circ} > 1^{\circ}$.