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

An element $X$ belongs to the $3rd$ period and group $16$ of the Modern Periodic Table.
$(a)$ Determine the number of valence electrons and the valency of $X$.
$(b)$ Write the molecular formula of the compound formed when $X$ reacts with hydrogen and draw its electron dot structure.
$(c)$ Name the element $X$ and state whether it is metallic or non-metallic.

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

The three elements $A$,$B$,and $C$ with similar properties have atomic masses $X$,$Y$,and $Z$ respectively. The mass of $Y$ is approximately equal to the average mass of $X$ and $Z$. What is such an arrangement of elements called? Give one example of such a set of elements.

The atomic numbers of three elements $A, B$,and $C$ are $12, 18$,and $20$ respectively. State,giving reason,which two elements will show similar properties.

$(a)$ Electropositive nature of the element$(s)$ increases down the group and decreases across the period.
$(b)$ Electronegativity of the element decreases down the group and increases across the period.
$(c)$ Atomic size increases down the group and decreases across a period (left to right).
$(d)$ Metallic character increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table,answer the following about the elements with atomic numbers $3$ to $9$:
$(a)$ Name the most electropositive element among them.
$(b)$ Name the most electronegative element.
$(c)$ Name the element with the smallest atomic size.
$(d)$ Name the element which is a metalloid.
$(e)$ Name the element which shows maximum valency.