Acatalyst is a chemical:

found in leaves
which promotes a chemical reaction
which reacts with sunlight
produced by the chloroplast

A catalyst is a chemical ,which promotes a chemical reaction.

Explanation:

A catalyst is a substance which speeds up a reaction without it being changed at the end of the reaction. Each reaction normally needs a specific amount of energy i.e. activation energy . The role of catalyst is to reduce that activation energy needed for a reaction occur.

"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."