First off its electron configuration is the following: [Ar]4s^2 3d^5 This can tell us a number of things about its valence electrons etc. You asked how many unpaired electrons. Plain and simple the answer is 5. Why? Well you might remember the diagram: __ __ __ __ __ __ 4s 3d since s orbitals only hold 2 electrons in them the 4s^2 is filled. In accordance with hund's rule and the pauli exclusion principle etc. We know that the two electrons in the s orbital will be paired. That only leaves 5 electrons in the 3d that we have to deal with. Now with proper use of Hund's rule and the Pauli exclusion principle, Afbau principle etc. we know that when we fill the electrons in the 3d we will put one on each line until we are FORCED to pair them. since there are five lines and five electrons none of these will be paired. Hence, there are only 5 unpaired electrons. The (II) refers to the oxidation state of the Mn. Most cases the (II) will be the s electrons since they will do most of the bonding. Remember that transition elements can be tricky and there is definitely no one rule to go by. Exceptions and cases and peculiarity abound.

Thank you! That was very helpful!