$A$ laboratory reagent imparts green colour to the flame. On heating with solid $K_2Cr_2O_7$ and conc. $H_2SO_4$,it evolves a red gas. Identify the reagent.

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 of the following is soluble in yellow ammonium sulphide?

When $H_2S$ gas is passed through the $HCl$ containing aqueous solutions of $CuCl_2$,$HgCl_2$,$BiCl_3$ and $CoCl_2$,which does not precipitate out?

Lead sulfate is soluble in which of the following?

The colour of the precipitate produced by adding $NaOH$ solution to $HgCl_2$ is