What is the reaction of sodium when it is introduced to water?

When sodium is introduced to water, the actual behavior observed is that it will react vigorously with the water, producing hydrogen gas and sodium hydroxide. This reaction is quite exothermic, meaning it releases a significant amount of heat.

The sodium will not only melt upon contact with the water (due to the heat from the reaction), but it also tends to form a spherical ball because the surface tension of the molten sodium will pull it into a more compact shape. Additionally, the hydrogen gas produced can catch fire due to the heat of the reaction, and the sodium may even skid across the surface of the water due to the formation of this gas.

While the choice indicates melting and becoming spherical, it doesn't fully encompass the vigorous reactivity of the sodium with water, and the potential for ignition due to the heat generated. Therefore, while the melting and shape change occur, the reaction itself is much more dramatic. Thus, this description alone does not accurately represent the entire phenomenon.