Use ArrayFlatten to get a 100X100 matrix:
Ev2 = ArrayFlatten[Ev]; Dimensions[Ev2] {100, 100}
ArrayPlot[Ev2] 
If I understand "code which takes any 10×10 matrix as the input, assigns value of i and j to its elements based on their position in the matrix" correctly, you can get a matrix of indices in several ways:
SeedRandom[1] n = 5; somematrix = RandomInteger[10, {n, n}]; positionsmat1 = Array[List, {n, n}]; positionsmat2 = Table[{i, j}, {i, n}, {j, n}]; positionsmat3 = MapIndexed[#2 &, somematrix, {2}]; Row[Grid[#, Dividers -> All] & /@ {somematrix, positionsmat1, positionsmat2, positionsmat3}, Spacer[10]] 