Question

All elements in a period have the same energy level due to which of the following reasons?

a. the same atomic number
b. the same number of neutrons
c. the same number of electrons
d. the same number of electron shells

Answer 1

The answer is D. Any element in the same period have the same number of electron shells.

For example, elements like Mg, Al and Na are all in period 3 and therefore they all have 3 electron shells.