Assertion (A) is correct because the sentence "The details of the incident" was not known” is grammatically incorrect due to subject-verb agreement. "Details" is plural, so the verb should be "were" instead of "was".
Reason (R) is also true. In constructions like "Noun + Preposition + Noun,” the verb agrees with the noun before the preposition (here, "details"), which is plural. Therefore, Reason (R) correctly explains why the sentence is grammatically incorrect.
List I | List II |
(A)Fits and starts | (1) At appropriate time |
(B)In less than no time | (II) At intervals |
(C) Once in a blue moon | (III) In a moment |
(D) On the dot | (IV) Rarely |