When acidified solution of potassium dichromate is shaken with aqueous solution of ferrous sulphate then

• The chromium ion has ability to accept the electrons and ferrous ion has ability to release the electrons.
• In this reaction the chromium ion oxidizes the ferrous ion and reduce itself into +3 ions.

         This process is called redox reaction.

$$\begin{gathered} {\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7 +6{\mathrm{FeSO}}_4+7{\mathrm{H}}_2{\mathrm{SO}}_4 \\ \to {\mathrm{K}}_2{\mathrm{SO}}_4 +{\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3+3{\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3 +7{\mathrm{H}}_2\mathrm{O} \end{gathered}$$