WHAT IS IT?  Temperature at which a source of ignition 1 cm above the surface of a liquid (in equilibrium with its vapor) will cause it to ignite.

acetone fl.p. = -17 C

diethyl ether fl.p. = -45 C

hexane fl.p. = -7 C

pentane fl.p = -40 C

chloroform has no fl.p.

water has no fl.p.