Which of the following sentence/sentences is/are incorrect?
(a) I will dine with them on next Sunday.
(b) He went to school but returned back immediately.
Answer options:

The correct answer is Option A (Both (a) and (b)).

Key Points:
• Superfluous words and redundant prepositions in English grammar.
• Option (1) - 'Both (a) and (b)' are incorrect.
• In sentence (a): Prepositions like 'on', 'in', or 'at' are NOT used before time expressions qualified by 'next', 'last', 'this', or 'every'. It should be 'I will dine with them next Sunday' (the use of 'on' is redundant and ungrammatical).
• In sentence (b): 'Return' itself means to come or go back. Using 'back' with 'returned' is an error of redundancy/superfluity (pleonasm). It should be 'returned immediately'.
• Hence, both sentences are incorrect.
• Key Takeaway: Never use 'on' before 'next Sunday', and never use 'back' after 'returned'.