Question 7
Which element has the electron configuration 2, 8, 8, 2?
The right answer is the one marked above.
Calcium. Add the numbers: 2 + 8 + 8 + 2 = 20, and an element's electron total equals its atomic number.
The same arithmetic identifies the others: neon is 2, 8; argon is 2, 8, 8; magnesium is 2, 8, 2. Adding up the configuration is the quickest way to name an element from it.