Calculation of oxidation state of Mn in Mncl2
 Mn – 25 	
1S2  2S2  2P6  3S2  3P6  3d5  4S2

Let the oxidation state of Mn in Mncl2 be X
Oxidation state of Cl is -1
X+[2x(-1)] = 0
X-2=0
X=2
Hence the oxidation state of Mn in Mncl2 is 2 and its
 electronic configuration is 1S2 2S2 2P6 3S2 3P6 3d5

So the electronic configuration of  MnO2 will be
 1S2  2S2  2P6  3S2  3P6  3d3
 
MnO2
Oxidation state of O is -2
X+[2x(-2)] = 0
X-4=0
X=4

Calculate the oxidation state of Mn in Mn2O3 and
 write the electronic configuration of Mn2O3

Calculate the oxidation state of Mn in Mn2O7 and write 
the electronic configuration Mn2O7

      
  

 Calculation of oxidation state of Fe in Fecl2
 
Fe – 26 	
1S2   2S2   2P6   3S2   3P6   3d6   4S2

Let the oxidation state of Fe in Fecl2 be X
Oxidation state of Cl is -1
X+[2x(-1)] = 0
X-2=0
X=2

Hence the oxidation state of Fe in FeCl2 is 2
So the electronic configuration of FeCl2 will be
 1S2   2S2   2P6   3S2   3P6   3d6 

FeCl3
Oxidation state of Cl is -1
X+[3x(-1)] = 0
X-3=0
X=3
Hence the oxidation state of Fe in FeCl3 is +3 and
 its electronic configuration is :
1S2 2S2 2P6 3S2 3P6 3d5