Final answer:
The Mn atom in the +3 state as in Mn₂O₃ has 4 unpaired electrons and is paramagnetic. In the +4 state as in MnO₂, it has 3 unpaired electrons. The Be₂²- ion has no unpaired electrons and is diamagnetic.
Step-by-step explanation:
The student asked about the number of unpaired electrons in a Mn atom. To answer this, one must look at the electron configuration of Mn, particularly in its common oxidation states. Manganese (Mn) has an atomic number of 25, which means in its neutral, ground state, it would have 25 electrons. The electron configuration for Mn is [Ar] 4s²3d⁵, which has 5 unpaired electrons.
In the question provided, Mn is in different oxidation states. Mn₂O₃, containing Mn in a +3 state, would have its electron configuration altered to [Ar] 4s⁰ 3d⁴, which leaves 4 unpaired electrons, making it paramagnetic. Similarly, MnO₂ contains Mn in a +4 state, and its electron configuration would be [Ar] 4s⁰ 3d³, with 3 unpaired electrons, meaning it's paramagnetic but less so than the Mn⁰¹³
For the Be₂²- ion the student is asking about, beryllium normally has two electrons in the 1s orbital. As a Be₂²- ion, it would have a total of 4 electrons, which would completely fill the 1s orbital with paired electrons. Therefore, there are no unpaired electrons, and Be₂²- would be diamagnetic.