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

Atomic radii of the elements of the second period are given below :

Period $II$ elements	$B$	$Be$	$O$	$N$	$Li$	$C$
Atomic radius $(pm)$	$88$	$111$	$66$	$74$	$152$	$77$

$(i)$ Arrange them in decreasing order of their atomic radii.
$(ii)$ Are the elements now arranged in the pattern of a period in the Periodic Table?
$(iii)$ Which elements have the largest and the smallest atoms?
$(iv)$ How does the atomic radius change as you go from left to right in a period?

$(a)$ How does electropositivity of elements get affected as we move :
$(i)$ down a group
$(ii)$ across a period?
$(b)$ Which atomic property increases both as we move across a period or down a group?

$Li, Be, B$ 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?

It was assumed by Newlands that only :

$K$ 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?