The oxidation state or oxidation number is defined as the loss or gain of electrons from an atom, molecule, or compound.

The reaction of potassium dichromate, potassium chloride and sulphuric acid (conc.)is as follows,

${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\left(\mathrm{s}\right)+4\mathrm{KCl}\left(\mathrm{s}\right)+6{\mathrm{H}}_2{\mathrm{SO}}_4 (\mathrm{conc}.)$

$\to 2{\mathrm{CrO}}_2{\mathrm{Cl}}_2\left(\mathrm{g}\right)+6{\mathrm{KHSO}}_4+3{\mathrm{H}}_2\mathrm{O}$

This reaction takes place in chromyl chloride test.

The Chromyl chloride is a neutral molecule as it does not have any charge on it.

Here, oxidation state of $\mathrm{Cr}$  in ${\mathrm{CrO}}_2{\mathrm{Cl}}_2$ is $+6$.