Question

Pt(s) | Mn2+(aq), MnO4-(aq), H+(aq) || H+(aq), IO3-(aq) | I2(s) | Pt(s)

Pt(s) | Mn2+(aq) | MnO2(s) | H+(aq) || H+(aq) || PbO2(s) | Pb2+(aq) | Pt(s)

how come the first one has comas within cell notation but not the second one,

Answer 1

Are you sure of the second one? It appears to have two salt bridges. || and ||

Answer 2

oops, the second one should be
Pt(s) | Mn2+(aq) | MnO2(s) | H+(aq) || H+(aq) | PbO2(s) | Pb2+(aq) | Pt(s)

but can you clarify the comma one

Answer 3

Commas separate multiple species in the same phase. The single bar is used to separate phases.