In the Modern Periodic Table,which are the metals among the first ten elements?

$Lithium$,$sodium$,and $potassium$ are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?

Nitrogen (atomic number $7$) and phosphorus (atomic number $15$) belong to group $15$ of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?

Which element has
$(a)$ a total of three shells,with four electrons in its valence shell?
$(b)$ a total of two shells,with three electrons in its valence shell?
$(c)$ twice as many electrons in its second shell as in its first shell?

Compare and contrast the arrangement of elements in Mendeleev's Periodic Table and the Modern Periodic Table.

Besides gallium,which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)