MnO2 + HCl --- MnCl2 + Cl2 + H2O BY oxidation method

FeS2 + O2 --- Fe2O3 + SO2 BY oxidation method

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Oxidation numbers of all elements are:

Change in oxidation number

Cl : -1 → 0  Net change = +1 So, the number of electrons lost by one Cl atom = 1

Mn : +4 → +2 Net change = -2 So, the number of electrons lost by one Mn atom = 2

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

Therefore, multiplying the formula containing Cl by 2 we get,

MnO₂ + 2HCl → MnCl₂ + Cl₂ + H₂O

In order to balance hydrogen, chlorine and oxygen atoms, we change the coefficient of HCl from 2 to 4 and H₂O from 1 to2.

MnO₂+ 4HCl → MnCl₂ + Cl₂ + 2H₂O

This is the balanced equation.