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

An aqueous solution of a salt $X$ turns blood red on treatment with $CNS^{-}$ and blue on treatment with $K_4[Fe(CN)_6]$. $X$ also gives a positive chromyl chloride test. The salt $X$ is

When calomel reacts with $NH_4OH$,we get

The incorrect statement out of the following is:

Which ion is detected using Nessler's reagent?

Which of the following pair of cations can be separated by excess $NaOH$ solution?