Final answer:
Sodium metal reacts with water to form hydrogen gas and an aqueous solution of sodium hydroxide due to the metal's high reactivity, which is characteristic of Group 1 metals.
Step-by-step explanation:
When sodium metal is introduced to water, a chemical reaction takes place, wherein the sodium reacts with water to produce hydrogen gas and sodium hydroxide (NaOH). In this exothermic reaction, sodium hydroxide, in its pure form a solid, dissolves in water forming an aqueous solution. This is because sodium hydroxide is a strong base and disassociates almost completely in water into sodium ions (Na+) and hydroxide ions (OH-), increasing the number of hydroxide ions in the solution.
This reaction is representative of the high reactivity of Group 1 metals with water, where the metal replaces the hydrogen in water, to form the corresponding metal hydroxide and hydrogen gas. The reaction can be vigorous and in the case of a large piece of sodium, it can generate considerable heat to the point of igniting the hydrogen gas produced.