Silver. For the most part only metals can have metallic bonding. Ammonium chloride has ionic bonding (poly-atomic cation + nonmetal=ionic bonding), iodine is a diatomic element so it will form a covalent bond with itself, and barium oxide has ionic bonding (metal+nonmetal or metal+poly-atomic anion=ionic bonding).
I hope this helps. Let me know in the comments if anything is unclear.
