An atom has electronic configuration $2$, $8$, $7$.

$(a)$ What is the atomic number of this element ?

$(b)$ To which of the following elements would it be chemically similar ?(Atomic numbers are given in parentheses.)

$N(7)$  $F(9)$  $P(15)$  $Ar(18)$

Element $X$ forms a chloride with the formula $XCl_2$, which is a solid with a high melting point. $X$ would most likely be in the same group of the Periodic Table as

By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic ?

$Ga$         $Ge$        $As$        $Se$       $Be$

In the Modern Periodic Table, which are the metals among the first ten elements ?

Which element has

$(a)$ two shells, both of which are completely filled with electrons?

$(b)$ the electronic configuration $2,\,8,\,2 ?$