What happens to electrons during an oxidation reduction reaction

A redox (reduction-oxidation) reaction involves transfer of electrons between two species.

Oxidation reaction involves loss of electrons and the species undergoing oxidation is termed as a reducing agent. Here loss of electrons is accompanied by an increase in the oxidation state/oxidation number.

Reduction reactions proceed via gain of electrons, the one undergoing reduction which is termed as an oxidising agent. Here the gain of electrons is accompanied by decrease in the oxidation state/oxidation number of that particular species.

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.