Question

explain how the element sodium is monovalent

Answer 1

Electronic configuration of sodium(Na)
= 1s2 2s2 2p6 3s1
Sodium has 1 electron in its outer most shell and to acquire noble gas configuration it will lose one electron and hence sodium is monovalent

Answer 2

Sodium is a metal with atomic number 11.
electronic configuration: 1s²2s²2p⁶3s¹
Number of valence electrons : 1

In order to get stability by acquiring octet configuration sodium prefers to loose 1 electron.

Hence Sodium valency is one --- Monovalent.