Which one of the following metals does not form amalgams ?

Iron does not amalgamate with mercury; official guidance explicitly cites iron as an exception to amalgamation with mercury [1]. More general chemical references state that mercury forms amalgams with most metals but lists iron (along with cobalt, nickel, platinum, tungsten and tantalum) as notable exceptions, because their surface properties and strong metallic bonding prevent mercury from dissolving into their lattices [2]. Zinc, copper and magnesium are not listed among these exceptions and are known to form amalgams under appropriate conditions (e.g., zinc amalgam in laboratory reductions), so the metal that does not form an amalgam here is iron (option 4).

Sources

1. [1] https://mpcb.gov.in/sites/default/files/biomedical-waste/Mercury_Waste_Generated03032020.pdf
2. [2] https://sciencenotes.org/amalgam-definition-and-uses-chemistry/