Which of the following gives a black precipitate when $H_2S$ gas is passed through its solution?

$A$ pink coloured salt turns blue on heating. The presence of which cation is most likely?

$A$ solution containing a group $IV$ cation gives a precipitate on passing $H_2S$ gas. $A$ solution of this precipitate in dilute $HCl$ produces a white precipitate with $NaOH$ solution and a bluish-white precipitate with basic potassium ferrocyanide. The cation is:

Which of the following is not correctly matched?

$A$ metal salt solution forms a yellow precipitate with potassium chromate in acetic acid,a white precipitate with dilute $H_2SO_4$,but gives no precipitate with $NaCl$. The metal salt solution will consist of:

Which ions can be separated using concentrated $NaOH$?