If Z = 3, what would be the valency of the element? Also name the element.

The symbol Z stands for the atomic number of an element. By saying that Z = 3, we mean that the atomic number of this element is 3. The electronic configuration of the element having atomic number 3 is K  L. 2,  1

It has 1 electron in its outermost shell (L shell). So, one atom of this element can lose 1 electron to achieve the nearest inert gas electron arrangement of K (which is the same 2 as that of helium gas). Since one atom of this element loses 1 electron to achieve the inert gas electron configuration, therefore, its valency is 1. The element having atomic number 3 is lithium.