An element $\mathrm{X}$ belongs to the second period and group $15$ of the periodic table. Find out the number of valence electrons in its atoms.

Arrange the following elements according to the instructions written in parenthesis.

$\mathrm{Cu}, \mathrm{Mn}, \mathrm{Ge}, \mathrm{Sc}$ (increasing atomic size)

Arrange the following elements according to the instructions written in parentheses.

$\mathrm{Fe}, \mathrm{Hs}, \mathrm{Ru}, \mathrm{Os}$ (increasing number of shells)

Arrange the following elements according to the instructions written in parenthesis.

$\mathrm{Hf}, \mathrm{Cs}, \mathrm{Ba}, \mathrm{Tl}$ (increasing valency)