20   mL of 0 . 02 MK 2 Cr 2 O 7 solution is used for the titration of 10   mL of Fe 2 + solution…

Equivalents of  ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7=$ Equivalents of ${\mathrm{Fe}}^{2+}$

$\Rightarrow$(Molarity $\times$ volume $\times$ $\mathrm{n}.\mathrm{f}$) of ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7=$ (molarity $\times$ volume $\times$ $\mathrm{n}.\mathrm{f}$) of ${\mathrm{Fe}}^{2+}$

$\mathrm{n}.\mathrm{f}=\mathrm{n}-\mathrm{factor}(\mathrm{valence} \mathrm{factor})$

$\Rightarrow 0.02\times 20\times 6=\mathrm{M}\times 10\times 1$

$\Rightarrow \mathrm{M}=0.24$

$\Rightarrow$ Molarity $=24\times {10}^{-2}$