A method for determining the quantity of dissolved oxygen in natural waters requires a series of redox reactions. Balance the following chemical equations in that series under the conditions indicated (and include phases):
a. in basic solution
Mn^(2+) (aq) + O2 (g) ---> MnO2 (s)
b. in acidic solution
MnO2 (s) + I^(-) (aq) ---> Mn^(2+) (aq) + I2 (s)
c. in neutral solution
I2 (s) + S2O3^(2-) (aq) ---> I^(-) (aq) + S4O6^(2-) (aq)