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

Taking the example of an element of atomic number $16$, explain how the electronic configuration of the atom of an element relates to its position in the modern periodic table and how valency of an element is calculated on the basis of its atomic number.

$Na, Mg, Al, Si, P, S, Cl$ and $Ar$ are the elements of the third period.
$(a)$ Which one of them is an inert gas? Why?
$(b)$ Which one of them has a valency of $4$? What kind of bond does it form: ionic or covalent?
$(c)$ Which of them are electropositive? Pick any two.

An element which is an essential constituent of all organic compounds belongs to :

Which of the following statement$(s)$ about the Modern Periodic Table are incorrect?
$(i)$ The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number.
$(ii)$ The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses.
$(iii)$ Isotopes are placed in adjoining group$(s)$ in the Periodic Table.
$(iv)$ The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number.

Three elements $A$, $B$, and $C$ have $3$, $4$, and $2$ electrons respectively in their outermost shell. Determine the group number to which they belong in the Modern Periodic Table and state their valencies.