Question

How many core electrons and valence electrons are present in ${}_{11}Na$?

• A. 10, 1
• B. 4, 7
• C. 2, 9
• D. 7, 4

Answer 1

The correct option is A 10, 1

Core electrons are the electrons which are in the completely filled shells. Basically the electrons present in the inner shell are core electrons.

Valence electrons are the electrons which are present in shells which are not completely filled. These electrons are added to the shell with highest principle quantum number (with exceptions) and has the highest energy level.

Electronic configuration of Na is $1s^{2}2s^{2}2p^{6}3s^1$

So, the number of core electrons are 10 as they have been completely filled shells.
Number of valence electrons = 1