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)?

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

An element $\mathrm{X}$ belongs to group $\mathrm{I}$ and third period of the periodic table. Find out:

(i) electron arrangement.

(ii) metal or non-metal.

(iii) name of the element.

Which has the larger atomic radius?

$\mathrm{Na}$ or $\mathrm{K}$