Which of the following elements does not lose an electron easily?

The electrons in the atoms of four elements $A, B, C$ and $D$ are distributed in three shells having $1, 3, 5$ and $7$ electrons in the outermost shell respectively. State the period in which these elements can be placed in the modern periodic table. Write the electronic configuration of the atoms of $A$ and $D$ and the molecular formula of the compound formed when $A$ and $D$ combine.

Study the following table in which positions of six elements $A, B, C, D, E$ and $F$ are shown as they are in the modern periodic table:

Group $\to$	$1$	$2$	$13$	$14$	$15$	$16$	$17$	$18$
Period $2$	$A$	-	-	-	$B$	-	-	$C$
Period $3$	-	-	$D$	$E$	-	-	-	$F$

On the basis of the above table,answer the following questions:
$(i)$ Name the element which forms only covalent compounds.
$(ii)$ Name the element which is a metal with valency three.
$(iii)$ Name the element which is a non-metal with valency three.
$(iv)$ Out of $D$ and $E$,which is bigger in size and why?
$(v)$ Write the common name for the family to which the elements $C$ and $F$ belong.

An element $X$ (atomic number $17$) reacts with an element $Y$ (atomic number $20$) to form a divalent halide.
$(a)$ Where in the periodic table are elements $X$ and $Y$ placed?
$(b)$ Classify $X$ and $Y$ as metal$(s)$,non-metal$(s)$,or metalloid$(s)$.

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.

Describe the basic character of the oxides of third period elements across the period from left to right.