What is an active metal? A. a metal that reacts with oxygen
B. a metal that is above hydrogen in the activity series
C. a transition metal
D. a metal with only one valence electron

A metal is said to be an active metal when it reacts strongly and quickly with other elements due to the electrons in its structure and its ease of sharing the electrons with other elements. ... A metal's reactivity increases as we go from the top to the bottom of the periodic table.

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."