What is the oxidation number for Mn in K2MnCl4?

Answer 1

The answer is +2 although understanding why is not so easy!

In compounds potassium is nearly always +1, so we have two of those in our compound giving +2.

Chlorine can exist in many oxidation states but as only oxygen and flourine are more electronegative than chlorine, and neither are present in our compound, we can assume that chlorine has the oxidation number of -1.

So we have two potassium (+1 x 2) and four chlorine (-1 x 4) this means that excluding the manganese atom we have a total of -2. In order for the compound to be balanced the manganese must be +2.