Final answer:
Liquid water (H₂O(l)) has a high specific heat capacity and therefore would retain heat for the longest period, making it suitable for insulation purposes where consistency of temperature is needed.
Step-by-step explanation:
To determine which substance would retain the most heat for the longest period, we need to consider the specific heat capacity of each substance. The substance with the highest specific heat will absorb more heat for a given mass and temperature change, hence will retain heat for longer. From the provided information, water in its liquid form (H₂O(l)) generally has a higher specific heat compared to other common substances like metals or ice (solid water). Therefore, H₂O(l) would experience the smallest temperature change after absorbing a certain amount of heat, indicating that it has the greatest specific heat and would retain heat for the longest period.
Conversely, metals like aluminum (Al(s)) and tin (Sn(s)) have lower specific heats, meaning they will heat up and cool down more quickly. Regarding a real-world application, an object with a large specific heat, like water, is ideal for insulation purposes where minimal thermal variation is desired.