Please help! Virtual Chemical vs Physical changes

Sometimes, it can be difficult to tell if a chemical or physical change is taking place. In the video, Dr. Jeff and the team explore a few different reactions to determine if they are chemical or physical changes, by figuring out if the material made after the reaction was present before the reaction. Chopping a banana.

Explanation:

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."