Complete the reaction:

Potassium dichromate and concentrated HCl are heated together. The chemical reaction taking place is

${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+\mathrm{HCl}\to \mathrm{KCl}+.....+.....+{\mathrm{H}}_2\mathrm{O}$

${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+14\mathrm{HCl}\to 2\mathrm{KCl}+2\mathrm{CrCl}{l}_3+7{\mathrm{H}}_2\mathrm{O}+3{\mathrm{Cl}}_2\uparrow$ is the exact balanced reaction of potassium dichromate and a concentrated acid results in evolution of chlorine gas.

The chromyl chloride test for the chloride anion, Cl^-, is the name given to this reaction.
The theory holds that heating a substance containing chloride (a solid salt, not a solution containing the solvated anion) in the presence of intense sulfuric acid and potassium dichromate results in the formation of chromyl chloride, a crimson fuming liquid.

In industrial and laboratory applications, potassium dichromate (K₂Cr₂O₇) is a chemical reagent that is typically employed as an oxidant. It is employed to oxidise primary alcohols and transform them into aldehydes and occasionally carboxylic acids. The only acids produced by permanganate-free procedures are carboxylic acids. There is no need for additional oxidation when the secondary alcohols are transformed into ketones. Tertiary alcohols are not oxidised by potassium dichromate. The substance is a crystalline ionic solid, vivid red-orange in colour, and may be hazardous to human health.

Hence, option D is correct.