Question

4s orbital is filled prior to 3d orbital but upon ionization 4s electrons get removed prior to 3d.why??

Answer 1

That's why electron of 4s shell areremoved first. ... As 4s orbitals have a lower energy than 3d orbitals,electrons are first filled in the 4s orbital and then in the 3d orbital. Whenelectrons are ionised, they are alwaysremoved from the outermost or valence shell.