The elements $A$,$B$,$C$,$D$,and $E$ have atomic numbers $9$,$11$,$17$,$12$,and $13$ respectively. Which pair of elements belongs to the same group?

Which of the following elements would form anions? Why?
$(i)$ $Na$ $(ii)$ $O$ $(iii)$ $Mg$ $(iv)$ $Al$ $(v)$ $Cl$

The element with atomic number $14$ is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?

Identify the elements with the following properties and arrange them in increasing order of their reactivity:
$(a)$ An element which is a soft and reactive metal.
$(b)$ The metal which is an important constituent of limestone.
$(c)$ The metal which exists in a liquid state at room temperature.

Which one of the following elements exhibits the maximum number of valence electrons?

The atomic numbers of a few elements are given below: $10, 20, 7, 14$.
$(a)$ Identify the elements.
$(b)$ Identify the group number of these elements in the Periodic Table.
$(c)$ Identify the periods of these elements in the Periodic Table.