Which of the following ions gives a white precipitate when $HCl$ is added to its aqueous solution?

On heating $NaCl + K_2Cr_2O_7 + \text{conc. } H_2SO_4$,the gas evolved is:

Nessler's reagent is used to detect

$A$ solution prepared in conc. $HCl$ sometimes gives white turbidity even in the absence of $1^{st}$ group,when water is added to it. It is due to the presence of

Which of the following ions forms a white precipitate upon the addition of $HCl$ to its aqueous solution?

$A$ 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: