Task: Question Answering
Input (English): Question: The determination of dissolved oxygen in natural water samples, using the Winkler method, is based on the previous oxidation of Mn (II) in an alkaline medium to: 
 Options:  <1> Mn (IV). <2> Mn (VI) <3> Mn (VII). <4> Mn (V). <5> Mn (I).
Output (English): 1