Consider the following reaction; Nitrite + Acetic acid + Thiourea  $\to {\mathrm{N}}_2\uparrow +{\mathrm{SCN}}^{-}+2{\mathrm{H}}_2\mathrm{O}$. The formation of the product in the above reaction can be identified by :

${\mathrm{FeCl}}_3/$ dilute HCI when blood red colour appears

${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7/\mathrm{HCl}$, when green colour appears

${\mathrm{FeCl}}_3/$ dilute HCI when blue colour appears

${\mathrm{KMnO}}_4/\mathrm{HCl}$, when colourless solution is formed