Which one among the following pairs of ions cannot be separated by $H_2S$ in dilute hydrochloric acid?

Which of the following statement$(s)$ is/are correct with reference to $Fe^{2+}$ and $Fe^{3+}$ ions?
$(1)$ $Fe^{3+}$ gives brown colour with potassium ferricyanide
$(2)$ $Fe^{2+}$ gives blue colour with potassium ferricyanide
$(3)$ $Fe^{3+}$ gives red colour with potassium thiocyanate
$(4)$ $Fe^{2+}$ gives brown colour with ammonium thiocyanate

On treating a solid salt $A$ with dil. $H_2SO_4$ and warming,reddish-brown fumes of gas $B$ are evolved. Addition of $C$ to the salt solution of $A$ followed by freshly prepared starch solution and acidification with acetic acid produces a blue colour. $C$ may contain:

$A \xrightarrow{ K_4[Fe(CN)_6] } \text{Blue-white precipitate}$. Which ion is $A$?

Among $Fe^{3+}$, $Pb^{2+}$, $Cu^{2+}$, and $Mn^{2+}$, identify the one that gets precipitated out while passing $H_2S$ gas in the presence of $NH_4OH$ as a group reagent. The highest possible oxidation state of the corresponding metal is:

What is formed when calomel $(Hg_2Cl_2)$ reacts with $NH_4OH$?