Explanation:
Sodium is the element having one valance electron and 3 energy level and is a metal.Its atomic number is 11 .So in first energy level ,there is 2 electrons ,in second energy level,there is 8 electrons and in third energy level,there is one electron.The one electron in the third energy level is called valance electron and it is a metal in the sence it has only one valance electron and it can easily loose it and gain +ve charge.
