Which class of fire extinguisher is appropriate for a fire involving a flammable liquid?
This is the black label isn't it; the carbon dioxide horn?
In your laboratory there will be posters on the wall that indicate the type of extinguisher to use on a particular fire. Mind you, in the event, most people tend to use whatever comes to hand. This is why it is important to aniticipate the type of fire you are likely to have, and what extinguishers (and where) are available.
Before the fire takes off (i.e. if you have a fume hood fire) the best extinguisher to use is liquid nitrogen. And you don't have to clean this up.