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

$A$ colourless crystalline salt $X$ is soluble in dilute $HCl$. On adding $NaOH$ solution,it gives a white precipitate which is insoluble in excess of $NaOH$. $X$ is

$A$ solution,when diluted with $H_2O$ and boiled,gives a white precipitate. On the addition of excess $NH_4Cl / NH_4OH$,the volume of the precipitate decreases,leaving behind a white gelatinous precipitate. Identify the precipitate which dissolves in $NH_4OH / NH_4Cl$.

Consider the following reaction scheme: $D(\text{White ppt}) \xleftarrow{Na_2CO_3} A \xrightarrow[\text{in acetic acid}]{K_2CrO_4} B(\text{Yellow ppt})$ and $A \xrightarrow{dil.\ H_2SO_4} C(\text{White ppt})$. If $A$ is a metallic salt,then the white precipitate $D$ must be:

Nessler's reagent is used to detect

$A$ light greenish coloured salt was soluble in water. On passing $H_2S$ into the solution,a black precipitate was obtained which dissolved readily in $HCl$. The metal ion present is: