Final answer:
Sodium metal is a soft, silvery-white, and very reactive alkali metal that conducts electricity and heat well and reacts vigorously with water.
Step-by-step explanation:
A piece of sodium metal can be described as a soft, silvery-white metal that is very reactive. Sodium, which is an alkali metal, has properties allowing it to conduct electricity and heat efficiently due to the 'sea' of delocalized electrons around the metal cations. In contact with water, sodium reacts vigorously, producing a basic solution of sodium hydroxide and hydrogen gas, the latter often igniting due to the heat generated in the reaction. Consequently, sodium is typically stored under oil to prevent these reactions by isolating it from moisture and air.