Arrange the following metals in decreasing order of their atomic size: $Ca, Mg, Ba, Be$.

Which of the given elements $A, B, C, D$ and $E$ with atomic numbers $2, 3, 7, 10$ and $30$ respectively belong to the same period?

Arrange the following elements in the order of their increasing nonmetallic character:
$Li, O, C, Be, F$

The element with atomic number $18$ belongs to which group?

Which one of the following elements exhibits the maximum number of valence electrons?

Given below are four elements with their atomic numbers:

Element	Atomic Number
$A$	$16$
$B$	$11$
$C$	$3$
$D$	$14$

$(a)$ Identify the elements which belong to the same group of the Modern Periodic Table.
$(b)$ Arrange the given elements in decreasing order of atomic size.
$(c)$ Write the formula of the oxide of $B$.
$(d)$ Which of the above elements is a metalloid?