Balance this redox reaction occurring in acidic media:

Cr2O7[2-] (aq) + Cl[-] (aq) Cr[3+] (aq) + Cl2 (g)

Add 7 water atom to the right hand side to adjust the quantity of oxygen. Increase Cr (+3) by two to adjust the quantity of Cr. Duplicate Cl-by two to adjust the quantity of chlorine molecules.

Cr2O7[2-] (aq) + 2 Cl[-] (aq) 2 Cr[3+] (aq) + Cl2 (g) + 7H2O

Presently adjust that charges.

you have - 4 charges on the left hand side, while + 18 charges on the right hand side, there for include 14H + the left hand side to adjust the charges

Cr2O7[2-] (aq) + 2 Cl[-] (aq) + 14H + 2 Cr[3+] (aq) + Cl2 (g) + 7H2O

take note of that the oxidation number of hydrogen in water is + 1