According to ISI, bitumen is classified into

ANS:E - 10 grades.

Option E is right.

Penetration, viscosity, oxide bitumen grade, bituminous binders prepration, cutback,
Fluxed, modified, emultion, asphalt, performence, natural. Whoever is saying 6, Please mention the IS code as I couldn't find any IS code which says there are 6 grades.
And please note that the question asked about the NUMBER of grades. It didn't tell anything about the nature of the classification. As per IS 73:1992. There are six penetration grade (S35, S45, S55, S65, S90&S200). And as per Is73:2013 there are 4 viscosity grade (VG10, VG20, VG30 & VG40). As per IS 73:2006 Cl-5, there's only 4 grade of bitumen. So, the correct answer will be B.4.