Arrange the following elements in the order of their increasing nonmetallic character:
$Li, O, C, Be, F$

Three elements $B$,$Si$ and $Ge$ are

Which one of the following does not increase while moving down the group of the periodic table?

Why are lithium (atomic number $3$) and potassium (atomic number $19$) placed in group $1$? What will be the atomic numbers of the first two elements in group $2$?

$(a)$ Identify the element that has two completely filled shells and the number of valence electrons in each are as: $(i)$ $1$,$(ii)$ $2$,$(iii)$ $7$,$(iv)$ $8$. $(b)$ Analyse which amongst them is inert.

An element belongs to the third period and second group of the periodic table:
$(a)$ State the number of valence electrons in it.
$(b)$ Is it a metal or a non-metal?
$(c)$ Name the element.
$(d)$ Write the formula of its oxide.