Explain why the quantum number set (2, 2, -1, -½) is not possible for an electron in an atom.

This quantum set is not possible because electrons cannot exist half way between two energy levels they needs discrete amount of energy to move from one energy level to the next and do not move until the exact amount is received so they can't be found at varying energy levels.

The reaction will shift to the right

You can still be friends with each other. you don't have to date since he likes someone else. just stick to being friends for now