Which of the following acts as catalyst in production of ammonia by Haber’s process?

Haber’s process:

i. Production of ammonia gas is carried out by Haber’s process.

ii. In this process, dihydrogen and dinitrogen are mixed together.

iii. They are passed over iron (Fe) catalyst to form ammonia.

iv. The reaction takes place given below:

Note: A catalyst is a substance which can change the speed of reaction without itself undergoing any change.