Usually three will be lost.
I believe 4s2 is the distinguishing (last) electron
Only three electrons.
Yttrium (Y) has, for the most part, 39 electrons. In its ion (atom with a charge that has lost or gained electrons) form though, it has 36 electrons.
Scandium (Sc), which has an atomic number of 21, can lose three electrons from its outermost shell, typically forming a +3 oxidation state. It typically does not gain electrons due to its position in the periodic table and its tendency to form metallic bonds. Thus, scandium primarily loses electrons rather than gaining them.
In the ion of barium, two electron are lost to follow the octet rule (to have a complete valence electron shell).
Scandium has 3 valence electrons.
Scandium has 3 valence electrons.
There is zero NET loss or gain of electrons
The element scandium has 21 electrons. However, most of these occupy the inner orbitals. The only electrons in the valence shell are those in the 2s orbital. Since there are two such electrons, scandium has 2 valence electrons.
Scandium has 1 3d electron.
Scandium typically has 21 electrons in a neutral atom. In an Sc3+ ion, it loses 3 electrons, so the ion would have 18 electrons.
I believe 4s2 is the distinguishing (last) electron
You can determine how many electrons are gained or lost by looking at the atom's charge. If the atom gains electrons, it becomes negatively charged; if it loses electrons, it becomes positively charged. The difference between the atom's original and final charge tells you how many electrons were gained or lost.
Only three electrons.
the oxidation number
If there are 4 electrons and 4 protons, the atom is electrically neutral since the positive charges from the protons balance out the negative charges from the electrons. No electrons are lost or gained in this scenario.
-3 electrons are gained,i.e,3 electrons are lost by Al and 3 electrons are gained by the other atom nearby.