Question

The number of shells in the elements of $3^{rd}$ period of the modern periodic table is-

• A. 1
• B. 2
• C. 3
• D. 5

Answer 1

The correct option is C

3

All the elements of the same group in a periodic table have the same number of valence electrons. Whereas all the elements of the same period have the same number of shells.
The outermost shell is called the valence shell; the period number refers to this shell.
Elements in the 3rd period will have 3 shells.
$\text{Na: [Ne]}3s^1$
$\text{Mg: [Ne]}3s^2$