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

The order of increasing atomic size is:

Arrange the following elements in the order of their decreasing metallic character:
$Na, Si, Cl, Mg, Al$

The position of three elements $A$, $B$, and $C$ in the Periodic Table are shown below:

Group $16$	Group $17$
-	-
-	$A$
-	-
$B$	$C$

$(a)$ State whether $A$ is a metal or non-metal.
$(b)$ State whether $C$ is more reactive or less reactive than $A$.

Write the trend of atomic size and metallic character along a group and a period in the modern periodic table.

Compare the radii of two species $X$ and $Y$. Give reasons for your answer.
$(a)$ $X$ has $12$ protons and $12$ electrons.
$(b)$ $Y$ has $12$ protons and $10$ electrons.