Nessler's reagent is used to detect

Which of the following sulphides is yellow in colour?

Concentrated aqueous $NaOH$ can separate a mixture of

On addition of aqueous $NaOH$ to a salt solution,a white gelatinous precipitate is formed,which dissolves in excess alkali. The salt solution contains

When $H_2S$ is passed through a solution in $Group-II$ analysis,it sometimes becomes milky. This indicates the presence of:

$A$ solution of a metal ion,when treated with $KI$,gives a red precipitate which dissolves in excess $KI$ to give a colourless solution. Moreover,the solution of the metal ion,on treatment with a solution of cobalt$(II)$ thiocyanate,gives rise to a deep blue crystalline precipitate. The metal ion is: