Question

Using the above periodic table, explain why:
- $Li$ and $Na$ are considered as active metals.
- Atomic size of $Mg$ is less than that of $Na$
- $F$ is more reactive than $Cl$

$H$							$He$
$Li$	$Be$	$B$	$C$	$N$	$O$	$F$	$Ne$
$Na$	$Mg$	$Al$	$Si$	$P$	$S$	$Cl$	$Ar$

Answer 1

The periodic table is the representation of chemical elements arranged in the increasing order of atomic numbers. The atomic radius increases along with the groups and decreases along the periods. The above periodic table given is the first three periods only.

Complete answer:
The chemical elements in the first group were known as alkali earth metals. These alkali earth metals have only one valence electron in their outermost shell and this one electron can be easily lost. Thus, these elements are known as active metals. Due to the presence of one valence electron, $Li$ and $Na$ are considered active metals.
While considering $Mg$ and $Na$ , these two elements belong to the same period. In periods, the atomic radius decreases along the period. Thus, the atomic size of $Mg$ is less than that of $Na$.
The elements in group $17$ are halogens, these are considered as non-metals. Fluorine is the most electronegative element in the periodic table. Due to this reason, fluorine is more reactive than chlorine, as fluorine has more tendency to attract electrons than chlorine.

Note:
The atomic size increases along with the group. Fluorine and chlorine belong to the same group. Due to the small size of the fluorine atom, it is more reactive than chlorine. Whereas while considering sodium and magnesium, these are in the same period.in periods the atomic size decreases due to the nuclear charge on outer electrons.