Hello! Your answer would be a gain of electrons and a decrease in positive charge.
Contrary to how it sounds, reduction is actually a gain of electrons. It is part of a set of reactions known as a redox reaction, reduction being a gain of electrons and oxidation being a loss.
With the gain of electrons, the element would become more negative as electrons bring with them a negative charge. Therefore, this would decrease the positive charge.
Hope this helped!
They discovered this since S waves don’t travel through the earth but P waves do. P waves tend to travel faster than S waves in speed, 1&14km/s vs 1&8km/s
