Option A - As the given sentence is a simple sentence, we can't use a question mark at the end of the sentence. Thus option A is incorrect.
Option C - As the given sentence is a simple sentence, we can't use an exclamation mark at the end of the sentence. Also, to show that the boy owns the room, we must use an apostrophe 's'. Thus option C is incorrect.
Option D - To show that the boy owns the room, we must use an apostrophe 's'. Thus option D is incorrect.
Option B - 'The boy's room is painted blue.' is correct as the sentence is a simple sentence and is punctuated with a full stop. Also, 'boy's' shows the ownership of the room. Thus option B is the correct answer.
'The boy's room is painted blue.'