In which reaction is there a transformation of mass into energy? For A P E X A. Two hydrogen atom fuse to form a helium atom

B. Ammonium nitrate breaks down into dinitrogen monoxide and water

C. Calcium oxide combines with water to form calcium hydroxide

D. Sodium combines with chlorine to form sodium chloride

"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.