Question

how to differentiate between primary, secondary and tertiary alcohols????

Answer 1

if i am right the "exception" is labelled as "methyl", don't take my word for it though.

Answer 2

using anoop's picture, we distinguish them by the number of carbon atoms connected to the carbon bearing the -OH group. why do we care about that? because it has to do with the stability of carbocations that could be formed from this, steric hindrance, etc.