Answer
Please see the work below.
Work Step by Step
We know that
$26.00mL\space soln\times \frac{0.025mol\space Cr_2O_7^{-2}}{1000mL\space soln}\times\frac{6mol\space Fe^{+2}}{1mol\space Cr_2O_7^{-2}}=3.90\times 10^{-3}mol\space Fe^{+2}$
Now $M=\frac{3.90\times 10^{-3}}{25.0\times 10^{-3}}=0.156M$
