Step 1: Analyzing the reaction.
Glycerol reacts with HCl, which leads to the formation of a product where an additional chlorine atom replaces one of the hydroxyl groups. The molecular formula of the product is \( \text{C}_3 \text{H}_8 \text{O}_4 \).
Step 2: Conclusion.
The correct product structure is \( \text{C}_3 \text{H}_8 \text{O}_4 \), corresponding to option (2).