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.

The atomic radii of the elements of the second period are given below:

Second period elements	$B$	$Be$	$O$	$N$	$Li$	$F$	$C$
Atomic Radii $(pm)$	$88$	$111$	$66$	$74$	$152$	$64$	$77$

$(i)$ Arrange these elements in decreasing order of their atomic radii.
$(ii)$ Are the elements now arranged in the pattern of a period in the periodic table?
$(iii)$ Name the element which has the $(a)$ smallest and $(b)$ largest atomic number.
$(iv)$ From the above data, infer how the atomic size or atomic radius of the elements changes as we move from left to right in a period.
$(v)$ Name one metal, one non-metal, and a metalloid out of these elements.
$(vi)$ Why does atomic radius decrease as we move from left to right in a period?

$K$ and $Ca$ have atomic numbers $19$ and $20$ respectively,and they belong to the same period.
$(a)$ Which among them would have a smaller atomic size?
$(b)$ Which one would be more electropositive?
$(c)$ To which group would each of them belong?

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

Study the following table in which positions of six elements $A, B, C, D, E$ and $F$ are shown as they are in the modern periodic table:

Group $\to$	$1$	$2$	$13$	$14$	$15$	$16$	$17$	$18$
Period $2$	$A$	-	-	-	$B$	-	-	$C$
Period $3$	-	-	$D$	$E$	-	-	-	$F$

On the basis of the above table,answer the following questions:
$(i)$ Name the element which forms only covalent compounds.
$(ii)$ Name the element which is a metal with valency three.
$(iii)$ Name the element which is a non-metal with valency three.
$(iv)$ Out of $D$ and $E$,which is bigger in size and why?
$(v)$ Write the common name for the family to which the elements $C$ and $F$ belong.

Name the element which has:
$(a)$ the electronic configuration $2, 8, 1$.
$(b)$ a total of two shells,with $4$ electrons in the valence shell.
$(c)$ a total of three shells,with $3$ electrons in the valence shell.
$(d)$ one shell which is completely filled with electrons.
$(e)$ twice as many electrons in the second shell as in the first shell.