Which of these belong to same period:

Element	Atomic number
$\mathrm{A}$	$2$
$\mathrm{B}$	$10$
$\mathrm{C}$	$5$

What is the basic difference in the electronic configurations of the elements belonging to group 1 and group 17? How do these help to explain different properties of the elements?

What is metallic character? How does it change in a period?

How do atomic radii change in a period and in a group?

An atom has the electronic configuration $2, 8, 7$. To which of the following element would it be chemically similar (atomic numbers are given)?

$\mathrm{N} \left(7\right), \mathrm{F} \left(9\right), \mathrm{P} \left(15\right), \mathrm{Ar} \left(18\right)$