The colour of tetrammine copper$(II)$ sulphate is

Select the incorrect match.

The iron salt used in blue prints is

The reagent used for the detection of $Ni^{2+}$ is $A$. $x$ moles of $A$ react with $Ni^{2+}$ to form a complex of $C$ color. $A$,$x$,and $C$ are respectively:

When potassium ferrocyanide crystals are heated with concentrated sulphuric acid,the gas evolved is

Which of the following is a chocolate brown complex?