Correct Answer: Fan – Blade

Solution : Let's check the options –
First option: Fan – Blade; Blade is the part of the fan. But, here fan should be the second word and blade be the first word.
Second option: Pedal – Cycle; Pedal is the part of the cycle.
Third option: Room – House; A Room is an integral part of the house.
Fourth option: Chapter – Book; A chapter is an integral part of the book.

So, the first option is different from the others. Hence, the first option is correct.