Which of the following metals is used as a catalyst in Haber's process of ammonia synthesis?

Iron is used as a catalyst in Haber's process.

The Haber process, also called the Haber Bosch process, is the industrial implementation of the reaction of nitrogen gas and hydrogen gas. It is the main industrial procedure to produce ammonia and the catalyst used is iron with a suitable promoter like ${\mathrm{K}}_2\mathrm{O}, \mathrm{CaO}, {\mathrm{SiO}}_2, \mathrm{and} {\mathrm{Al}}_2{\mathrm{O}}_3.$

Hence, Iron is used in the Haber cycle as a cheap catalyst because it allows in acceptable time to reach a reasonable yield