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.)

$N(7)$  $F(9)$  $P(15)$  $Ar(18)$

Why do you think the noble gases are placed in a separate group ?

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

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

Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice ?

Which element has

$(a)$ a total of three shells, with four electrons in its valence shell?

$(b)$ a total of two shells, with three electrons in its valence shell?

$(c)$ twice as many electrons in its second shell as in its first shell?