One flask immediately emits a gas once the stopper is removed what does the flask contain a. acetone b. diethyl ether c. butane d. chloroform

The answer is; C

This is due to the fact that the boiling point of butane is -5 degrees centigrade. These elements evaporate at room temperature (room temperature is usually around 20 degrees centigrade) which is past the boiling point of butane. A substance turns to gas when it passes it boiling point temperatures hence butane seems to sublimate when its flask is opened.  

he is very short, and he can only reach halfway up on the elevator buttons. but on a rainy day, he has his umbrella with him, and he uses it to poke the button at the top.