The ground state electron configuration of scandium is express your answer in condensed form, in order of increasing orbital energy. for example, [he]2s22p2 would be entered as [he]2s^22p^2.

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.

Answer the same molecular formula;

The answer is a. that is an exothermic reaction which means it produces heat