Arrange the following elements in the order of their decreasing metallic character: $Na, Si, Cl, Mg, Al$.

Justify the following statements:
$(a)$ Cations are smaller in size than the corresponding neutral atom.
$(b)$ The size of the atom increases as we move down a group.
$(c)$ Atomic size decreases as we move across a period.

Arrange the following metals in decreasing order of their atomic size: $Ca, Mg, Ba, Be$.

$Li, Be, B$ and $C$ are the elements of the same period of the Modern Periodic Table.
$(a)$ Arrange them in increasing order of their atomic size.
$(b)$ In which shell (number) would the last electron enter for all of them?
$(c)$ Calculate the number of valence electrons in each.
$(d)$ Which element amongst them is most electropositive?

An element $A$ has an atomic number $16$. To which group and period does it belong?

What property do all elements in the same column of the Periodic Table as boron have in common?