When KI is added to acidified solution of sodium nitrite :
Reduction of the acid gives different products, depending on the reducing agent.
With I− and Fe2+ ions, NO is formed.
NaNO2+KI+H2SO4→H2O+I2+K2SO4+NO+Na2SO4
2NaNO2+2FeSO4+2H2SO4→Fe2(SO4)3+2NO+2H2O+Na2SO4