Question

Assertion : The carbon atoms of the benzene ring may be numbered for identification of substituent groups, just as a continuous chains of carbon atoms arc numbered. 

Reason : Smallest set of numbers designating the substituents is the preferred set.

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not correct explanation of A

(c) A is true but R is false

(d) A and R are false

Answer 1

Correct option (b) Both A and R are true but R is not correct explanation of A

Explanation:

Nomenclature in benzene ring :

For only one substituent. no numbering is required. According to latest IUPAC system of nomenclature, the lowest set of locants is preferred even if it violates the lowest sum rule. 

1, 3-dimethylbenzene is preferred  as it corresponds  to smallest total set of numbers.