`Fe^(2+)(aq.)+Cr_(2)O_(7)^(2-)+H^(+) to Fe^(3+)(aq.)+Cr^(3+)`

Explanation

Step -1,2

For equation multiplied with 6 and `Cr_(2)O_(7)^(-2)` equation multiplied with 1
`6Fe^(2+)+overset(+6)(Cr_(2)O_(7)^(2-)) to 6Fe^(3+)+2Cr^(3+)`
Balance all the atoms other than O and H `6Fe^(2+)+Cr_(2)O_(7)^(2-) to 6Fe^(3+)+2Cr^(3+)`
Balance the O by adding `H_(2)O` molecule
`6Fe^(2+)+Cr_(2)O_(7)^(2-)+14H^(+) to 6Fe^(3+)+7H_(2)O`