Q4. Classify C6H5CH=CHC(CH3)2OH completely: by the number of –OH groups, by the carbon bearing –OH, and as allylic, benzylic or neither.
Monohydric. The –OH carbon carries three carbons (two CH3 and the CH= carbon), so it is 3°. It is next to the C=C double bond, so it is allylic; it is not next to the ring, so it is not benzylic (NCERT Intext Question 7.1 (vi), page 195; NCERT pages 194–195; reasoned).
Q5. How many –OH groups do benzene-1,3-diol (resorcinol) and propane-1,2,3-triol (glycerol) have, and how is each classified?
Resorcinol has two –OH groups on a benzene ring: a dihydric phenol. Glycerol has three on an open chain: a trihydric alcohol (NCERT pages 194–195; names from NCERT pages 196–197).
Q6. Why is CH2=CH–OH not an allylic alcohol, though it contains a C=C bond?
In an allylic alcohol the –OH is on the sp3 carbon next to the C=C. In CH2=CH–OH it is on one of the C=C carbons themselves, which is sp2: a vinylic alcohol (NCERT pages 194–195).