Which ion is detected using Nessler's reagent?

The reagent used for the identification of $Ni^{2+}$ ions is .....

Aqueous solution of which of the following cation gives a precipitate with potash alum?

$A$ reagent used to test the presence of $Fe^{2+}$ ion is

Which reagent is used to test for the presence of the $Fe^{+2}$ ion?

$M^{n+}(aq.) + KI \to X\downarrow \text{ (ppt.)}$ $\xrightarrow{Excess KI} \text{ppt. remains insoluble in excess } KI \text{ solution. Then cation } M^{n+}(aq.) \text{ can be}$