How many vertical columns are there in the modern periodic table and what are they called?

Three elements $X$,$Y$,and $Z$ have atomic numbers $7$,$8$,and $9$ respectively.
$(a)$ State their positions (Group number and period number both) in the Modern Periodic Table.
$(b)$ Arrange these elements in the decreasing order of their atomic radii.
$(c)$ Write the formula of the compound formed when $X$ combines with $Z$.

What would be the nature of oxides formed by the elements on the right-hand side of the periodic table?

$Li, Be, B$ 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?

Predict the maximum number of valence electrons possible for atoms in the first period of the periodic table.

Explain the basic character of oxides of elements down the group and across the period.