[winspice]

Mn (OH)2 + O2 ---> Mn (OH)3


Thanks.

[Borek]

Do it the same way - start with water on the left.

What O₂ can be reduced to?

[opti384]

First figure out which is reduced and which is oxidized.

[AWK]

Source of hydrogen (in this case - water) is missing on the left side

[research]

as I know you have 2 way to balance this equation 1-ion electron method    2-oxidation number method.
the first is when you want to balance a reaction which is held in a basic solution (like your desired reaction)first of all write your half reactions and balance the atoms which had changed their oxidation numbers then add O and H in this way: you should add H2O on the site of reaction with oxygen shortage for every O add one H2O molecule, then for every H shortage add a OH^- to that site and a H2O to the opposite site (this is for basic solutions only), then balance the number of electrons in both half reactions and finally multiple that half reactions with each other to obtain your balanced reaction.
for clarifying this explanation take a look at general chemistry by Mortimer chapter 13 named chemical reactions in water