what is the electron configuration for Na?

1) how many electrons are in each energy level of the following elements? a. he b. na c. na d. ne 2) how many valence electrons are percent in the following atoms? a. s b. mg c. be d. cl 3) which of the following elements are stable as atoms? a. he b. o c. cl d. ar if you are able to provide the work as to how you got the answers that would be greatly appreciated. : )

This image is an example of a(n) a) atom. b) compound. c) mixture. d) molecule.

What happens to isotopes that are unstable?