Which substance is a liquid at room temperature and would rapidly evaporate if left exposed to the air at this temperature? a. melting point (mp) -120 degrees celsius; boiling point (bp) -40 degrees. b. mp -5; bp 30. c. mp -8; bp 120. d. mp 10; bp 280. e. mp 660; bp 2450. What is the answer? Why is it correct but not the others?

Choice B is the correct answer.  That will be a liquid at room temperature, and it will evaporate quite quickly.  Room temperature is generally considered 20 degrees Celsius.  Choice B melts from a solid to a liquid at -5 degrees, so it's a liquid at room temperature as long as the boiling point is higher than 20 degrees.  It is.  The boiling point listed is 30 degrees, which is close to assumed room temperature.  Because the boiling point is so close to room temperature, it will evaporate into a gaseous state much more quickly than choices C and D.  Both of those will be liquid at room temperature, but their boiling points are much higher; therefore, they won't evaporate as quickly.  
Choice A is already a gas at room temperature, and choice E is still a solid at room temperature.  
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch14/melting.php