In a solution containing $Hg^{2+}, Cd^{2+}, Sr^{2+}, Fe^{2+},$ and $Cu^{2+}$ ions in $0.3 \, M \, HCl$,which ions will precipitate upon the addition of $H_2S$?

$Pb^{2+}$,$Cu^{2+}$,$Zn^{2+}$,and $Ni^{2+}$ ions are present in a given acidic solution. On passing hydrogen sulphide gas through this solution,the precipitate formed will contain:

In which of the following is $NH_{3}$ not used?

Consider the following sequence of reactions:
$M^{2+}(aq.)$ $\xrightarrow{NH_4Cl(s) + (NH_4)_2CO_3 \, sol.} Q \downarrow$ $\xrightarrow[\text{Followed by addition of } (NH_4)_2C_2O_4]{CH_3COOH} R \downarrow$
Which of the following cations can form precipitate $Q$ but does not form precipitate $R$?

Which reagent can be used to identify nickel ion $(Ni^{2+})$?

To a solution of a substance,gradual addition of ammonium hydroxide results in a black precipitate which does not dissolve in excess of $NH_4OH$. However,when $HCl$ is added to the original solution,a white precipitate is formed. The solution contained