Which kind?

Mpemba effect

first briefly Image solution

The Mpemba effect, named after Erasto Batholomeo Mpemba (b.1950) in 1963, is the observation that, in some circumstances, warmer water can freeze faster than colder water. Although there is some conflicting published support for the effect, there is disagreement on exactly what the effect is and under what circumstances it occurs. There have been reports of similar phenomena since ancient times, although allegedly with insufficient detail for the claims to be replicated. A number of possible explanations for the effect have been proposed.

There exists a set of initial parameters, and a pair of temperatures, such that given two bodies of water identical in these parameters, and differing only in initial uniform temperatures, the hot one will freeze sooner.

However, even with this definition it is not clear whether "freezing" refers to the point at which water forms a visible surface layer of ice; the point at which the entire volume of water becomes a solid block of ice; or when the water reaches $\text({0}^{°}{C}){32}^{°}{f}$ . A quantity of water can be at $\text{32}^{°}{f}$ and not be ice; after enough heat has been removed to reach $\text({0}^{°}{C}){32}^{°}{f}$ more heat must be removed before the water changes to solid state (ice), so water can be liquid or solid at $\text({0}^{°}{C}){32}^{°}{f}$ .

With the above definition there are simple ways in which the effect might be observed: For example, if the hotter temperature melts the frost on a cooling surface and thus increases the thermal conductivity between the cooling surface and the water container. On the other hand, there may be many circumstances in which the effect is not observed.

test image .

Hence the answer is $\color{#D61F06}{Warmer Water}$ .

fun image