Finding Possible Mismatch between columns

Does this help?

Sub ankituc()
Dim i As Long, r As Range, x As Range
With Application
    .Calculation = xlCalculationManual
    .ScreenUpdating = False
End With
For i = 2 To Range("A" & Rows.Count).End(3).row
    Set r = Columns(3).Find(Cells(i, "A").Value, LookIn:=xlValues, lookat:=xlPart)
    If Not r Is Nothing Then
        Cells(i, "A").AddComment "In Column C as: " & Cells(r.row, "C")
        Cells(i, "A").Interior.ColorIndex = 6
        Cells(r.row, "C").Interior.ColorIndex = 6
    End If
    Set r = Nothing
Next i
For i = 2 To Range("C" & Rows.Count).End(3).row
    Set x = Columns(1).Find(Cells(i, "C").Value, LookIn:=xlValues, lookat:=xlPart)
    If Not r Is Nothing Then
        Cells(x.row, "A").AddComment "In Column C as: " & Cells(i, "C")
        Cells(x.row, "A").Interior.ColorIndex = 6
        Cells(i, "C").Interior.ColorIndex = 6
    End If
    Set x = Nothing
Next i
With Application
    .Calculation = xlCalculationAutomatic
    .ScreenUpdating = True
End With
End Sub