How many 'd' electrons are present in `Cr^(2+)` ion?

How many electrons are present in Mg^(2+) ion?

How many electrons are present in the O ^(2-) ion ?

How many unpaired electrons are present in Mn^(2+) ion ? How do they influence magnetic behaviour of Mn^(2+) ion?

How many electrons are present in sulphur ?

How many electrons are present in sulphur ?

How many upaired electrons are present in Ni^(2+) ?

How many unpaired electron are present Co^(3+) ion?