Give one standard test of carbon dioxide and also write the equation involved is it a physical or a chemical change ? what is the answer for this

The reaction involved is: Carbon dioxide gas combines with calcium carbonate (lime water) to form, calcium carbonate and water. It is a chemical change because the substance has transformed into a new substance, having different chemical composition.

"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."

it's c. elements are placed in rows based on how may valencies electrons have.