Question

4s2 is the configuration of the outermost orbit of an element. It's atomic number would be?

Answer 1

it's atomic number is 20 or 30

Answer 2

Answer : The atomic number will be 20 and  element is Calcium.

Explanation :

The given configuration of outermost orbit of an element is, $4s^2$.

In the given configuration, Principle quantum number is '4' which represents the period in the periodic table and the number of electrons in valence shell is '2' which represents the group in the periodic table. So, the element will be Calcium according to the periodic table.

The electronic configuration of Calcium is,

$1s^22s^22p^63s^23p^64s^2$

The total number of electrons in calcium = 2 + 2 + 6 + 2 + 6 + 2 = 20

Atomic number = Number of electrons = 20

Therefore, the atomic number will be 20 and  element is Calcium.