Among the following number of examples for irreversible reactions are ________ . 

i) Combustion reactions 

ii) Haber’s process 

iii) Contact process 

iv) Decomposition of ammonium nitrate

All combustion reactions are exothermic and they are irreversible. Decomposition of ammonium nitrate is an irreversible reaction.

${\mathrm{NH}}_4{\mathrm{NO}}_3\to {\mathrm{N}}_2\mathrm{O}+2{\mathrm{H}}_2\mathrm{O}$

Note: Both Haber’s process and contact process are reversible reactions.

${\mathrm{N}}_2+3{\mathrm{H}}_2\rightleftharpoons 2{\mathrm{NH}}_3$