For the redox reaction:

${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}+{\mathrm{H}}^{\oplus }+\mathrm{Ni}⟶{\mathrm{Cr}}^{3+}+{\mathrm{Ni}}^{+2}+{\mathrm{H}}_2\mathrm{O}$

The correct coefficients of the reactants for the balanced reaction are

$C{r}_2{O_7}^{2-}$

Ni

${\mathrm{H}}^{\oplus }$

$\begin{array}{l}14{\mathrm{H}}^{\oplus }+\cancel{6{\mathrm{e}}^{-}}+{\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}\stackrel{ }{\to }{2\mathrm{Cr}}^{3+}+7{\mathrm{H}}_2\mathrm{O}\\ 2\mathrm{x}-14=-2 2\mathrm{x}=6\\ 2\mathrm{x}=12\\ \left. \mathrm{Ni}\stackrel{ }{\to }{\mathrm{Ni}}^{+2}+\cancel{2{\mathrm{e}}^{-}}\right]\times 3\\ 14{\mathrm{H}}^{\oplus }+{\mathrm{CrO}}_7^{2-}+3\mathrm{Ni}\stackrel{ }{\to }2{\mathrm{Cr}}^{3+}+3{\mathrm{Ni}}^{2+}+7{\mathrm{H}}_2\mathrm{O}\end{array}$