The answer is the third one .
Answer: aldehyde
Explanation: aldehyde has functional group R—CHO
Metal radiator. When hot water flows through the coils of the radiator , the metal heats up quickly by conduction and then radiates thermal energy into the surrounding air.
Answer: Metal radiator
There are many combinations because it is not all about the number of chemicals, but also about the size of the strand. The longer the strand the more combinations there are and more variations and various lengths provide various results.