Scandium is a d-Block element with atomic number 21. So, it has 21 protons and 21 electrons in neutral state. Electronic Configuration for Sc is,
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹
Also we know that,
Electronic configuration of Argon with atomic number 18 is,
[Ar] = 1s², 2s², 2p⁶, 3s², 3p⁶
Now comparing both configurations,
[Ar], 4s², 3d¹
This is condensed electronic configuration of Scandium.