Ferric ion forms a prussian blue precipitate due to the formation of

$\left[\mathrm{X}\right]+$ dil. ${\mathrm{H}}_2{\mathrm{SO}}_4⟶\left[\mathrm{Y}\right]:$ Colourless, suffocating gas

$\left[\mathrm{Y}\right]+{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+{\mathrm{H}}_2{\mathrm{SO}}_4⟶$ Green colouration of solution

Then, $\left[\mathrm{X}\right]$ and $\left[\mathrm{Y}\right]$ are