Ethanol shows turbidity with Lucas reagent (Conc. HCl + Anhyd. ZnCl₂).

The correct option is Upon heating.

Image Analysis:
As shown in the reaction equation in the image, ethanol reacts with concentrated hydrochloric acid in the presence of anhydrous zinc chloride:
$$C_2{H}_{5}OH+\text{HCl}\underset{\text{Δ}}{\overset{{\text{Anhyd. ZnCl}}_2}{\to }}{C}_2{H}_5\mathrm{Cl}+H_{2}O$$
The Greek symbol delta ($\Delta$) below the reaction arrow explicitly represents the application of heat.

Explanation of Lucas Test Reactivity:
Lucas reagent is a solution of anhydrous zinc chloride (${\text{ZnCl}}_2$) in concentrated hydrochloric acid ($\text{HCl}$). It is used to classify low molecular weight alcohols as primary, secondary, or tertiary based on their rate of reaction:
1. Tertiary Alcohols: Form a highly stable tertiary carbocation intermediate. They react immediately with Lucas reagent to produce insoluble alkyl halides, forming turbidity instantly at room temperature.
2. Secondary Alcohols: Form moderately stable secondary carbocations. They show turbidity within 5 to 7 minutes at room temperature.
3. Primary Alcohols: Ethanol ($C_2{H}_{5}OH$) is a primary alcohol. Due to the very low stability of primary carbocations, primary alcohols do not undergo substitution readily at room temperature. Thus, they show no reaction at room temperature and produce turbidity only upon heating.