Cr₂O_7^2-+ SO_{3^{2-GIVES RISE TO}} Cr³⁺SO₄ ^2-

^{BALANCE BY OXIDATION NUMBER METHOD}

Oxidation numbers of all elements are:

Change in oxidation number

Cr : +6 → +3  Net change = +1 So, the number of electrons gained by one Cr atom = 3
S: +4 → +6   Net change = -2 So, the number of electrons lost by one S atom = 2

Now, number of electrons gained and lost should be same:

Therefore, multiplying the formula containing Cr by 2 and S by 3 we get,

Balance oxygen atoms by adding H⁺ ions and H₂O molecules on the required sides of the equation:

This is the balanced equation.