The solid laboratory reagent A gives the following reactions :
I. It imparts green colour to the flame.
II. Its solution does not give a precipitate on passing ${\mathrm{H}}_2\mathrm{S}$

III. When it is heated with solid ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ and concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$, a red gas is evolved. When this gas is passed into aqueous solution of $\mathrm{NaOH}$ it turns yellow :
Identify A.

When handled with  ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ and conc ${\mathrm{H}}_2{\mathrm{SO}}_4,{\mathrm{Ba}}^{2+}$ ion gives green colour to the flame and Cl ion produces chromy chloride (which is orange red in colour).

$\begin{array}{l}{\mathrm{Ba}}^{2+}+2{\mathrm{Cl}}^{-}\to {\mathrm{BaCl}}_2\\ 2{\mathrm{BaCl}}_2+{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+3{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{K}}_2{\mathrm{SO}}_4+2{\mathrm{BaSO}}_4+2{\mathrm{CrO}}_2{\mathrm{Cl}}_2+3{\mathrm{H}}_2\mathrm{O}\end{array}$The following reactions are produced by a solid laboratory reagent (A).

${\mathrm{Cl}}^{-}+{\mathrm{C}}_2{\mathrm{O}}_7^{2-}\stackrel{H^{+}}{\to }{\mathrm{CrO}}_2{\mathrm{Cl}}_2\uparrow$

There is no precipitate obtained on passing ${\mathrm{H}}_2\mathrm{S}$ in its solution.

${\mathrm{CrO}}_2{\mathrm{Cl}}_2+4\mathrm{NaOH}\to {\mathrm{Na}}_2{\mathrm{CrO}}_4+2\mathrm{NaCl}+2{\mathrm{H}}_2\mathrm{O}$