Submerged soils have redox potential (Eh) around:

Correct option is C

· Flooded soils become reduced, lowering Eh to 0 to −300 mV.
· Leads to:
· Fe³⁺ → Fe²⁺
· Mn⁴⁺ → Mn²⁺
· Methanogenesis
Why other options are wrong
· (a) +700 mV = highly oxidized.
· (b) +300 mV = mildly oxidized soil.
· (d) −700 mV = extremely reduced, uncommon in fields.