Indentation is a bit off, but I tested it after reformatting using individual values and it is fine.
I suspect that the !Index1! field is the field you are trying to put the values IN and not the field that contains the Density values... check that
Python parser, as before
def Reclass(Density_18):
if (Density_18 <= .8493):
return 1
elif (Density_18 >.8493 and Density_18 <=1.761):
return 2
elif (Density_18 >1.761 and Density_18 <=2.345):
return 3
elif (Density_18 >2.345 and Density_18 <=3.399):
return 4
elif (Density_18 >3.399):
return 5
Reclass(Density_18)
3
Density_18 = .1
Reclass(Density_18)
1