Three elements $B$,$Si$ and $Ge$ are

$Na, Mg, Al, Si, P, S, Cl$ and $Ar$ are the elements of the third period.
$(a)$ Which one of them is an inert gas? Why?
$(b)$ Which one of them has a valency of $4$? What kind of bond does it form: ionic or covalent?
$(c)$ Which of them are electropositive? Pick any two.

Write true or false for the statement: The term atomic size refers to the distance between the centre of the nucleus and the penultimate shell of an isolated atom.

Write true or false for the statements: Non-metals are electronegative. They tend to form bonds by gaining electrons. As the trends in the electronegativity show,non-metals are found on the right-hand side of the periodic table towards the top.

Write the formulae of chlorides of Eka-silicon and Eka-aluminium,the elements predicted by Mendeleev.

Which of the following sets of elements is written in the order of their increasing metallic character?