i. We _______________ the room with an electric heater.
ii. His mother _______________________ lunch for all his friends.
iii. The will ______________________ the each child will receive half of the money.
iv. He __________________________ for his family by working overtime.

We _______________ the room with an electric heater. In this sentence, prepared cannot be used and thus, prepared is rejected.
His mother _______________ lunch for all his friends. In this sentence, equipped  cannot be used and thus, equipped is rejected.
He _______________ for his family by working overtime. In this sentence, arranged cannot be used and thus, arranged is rejected.
Hence, only provided is can be appropriately used in all the 4 sentences.
Hence, option D is the correct answer.