''Elements in Periodic Table show periodicity of properties.'' List any four such properties.

Properties of the elements are given below. Where would you locate the following elements in the periodic table?
$(a)$ An element which is an inert gas with atomic number $2$.
$(b)$ An element whose thin oxide layer is used to make other elements corrosion resistant by the process of 'anodising'.

Name any two elements which were discovered later after Mendeleev's periodic table.

Arrange the following elements in the increasing order of their metallic character:
$Mg, Ca, K, Ge, Ga$

Write true or false for the statement: Electronic configuration of hydrogen resembles that of alkaline earth metals.

An element $X$ belongs to the $3rd$ period and group $13$ of the Modern Periodic Table.
$(a)$ Determine the valence electrons and the valency of $X$.
$(b)$ Determine the molecular formula of the compound formed when $X$ reacts with an element $Y$ (atomic number $= 8$).
$(c)$ Write the name and formula of the compound formed when $X$ combines with chlorine.