Study the following unbalanced redox reaction. Which one of the following choices represents the balanced redox equation?

PbS + O2→ PbO + SO2

PbS + 2O2→ PbO + 2SO2

2PbS + 2O2→ 2PbO + 2SO2

2PbS + 3O2→ 2PbO + 2SO2

3PbS + 3O2→ 2PbO + 2SO2

You only need to count the number of atoms of each element in both sides of the equation. To be balanced, the number of each kind of atom has to be equal in the two sides.

Only the fourth equation, 2PbS + 3O2→ 2PbO + 2SO2, complies that:

Element Left side Right side

Pb 2 2

S 2 2

O 3*2=6 2 + 2*2 = 2 + 4 = 6