Why does Scandium have a 3 plus charge?

• Scandium is a d-block element.
• Its atomic number is $21.$
• The electronic configuration is $1s^{2}2s^{2}2p^{6}3p^{6}3d^{1}4s^2.$
• If Scandium acquires a +3 oxidation state i.e., loses 3 electrons, the electronic configuration becomes $1s^{2}2s^{2}2p^{6}3p^6$.
• This electron configuration is that of Argon which is a noble gas. This electronic configuration is most stable.
• Noble gas configuration is most stable as the orbitals are completely filled.
• Hence, Scandium has a 3 plus charge.