Answer:
the number of donated valence electrons
Step-by-step explanation:
A metallic bond is formed when atoms come together in a metallic crystal lattice.
The metal atoms are usually ionized such that in a metallic crystal lattice consists of metal ions and a sea of mobile electrons. Attraction between these positively charged ions and the sea of electrons constitutes the metallic bond.
Hence, the more the number of donated valence electrons, the stronger the metallic bond.