Read the given passage and answer the questions that follow :
Potassium chlorate, when heated strongly decomposes slowly giving dioxygen. The decomposition occurs in the temperature range of 653-873 K.
`2KClO_3 overset("Heat")to 2KCl + 3O_2`
However, when a little of manganese dioxide is added, the decomposition takes place at a considerably lower temperature range, i.e., 473-633 K and also at a much accelerated rate. The added manganese dioxide remains unchanged with respect to its mass and composition. In a similar manner, the rates of a number of a chemical reactions can be altered by the mere presence of a foreign substance.
The systematic study of the effect of various foreign substances on the rates of chemical reactions was first made by Berzelius, in 1835. He suggested the term catalyst for such substances.
Give another example of a reaction and the catalyst used in the reaction.

Explanation

`N_2(g) + 3H_2(g) underset(Mo(s))s overset(Fe(s))to 2NH_3(g)`