For a substance to change from a gas to a liquid what must happen to its particles A. they must lose enough of their kinetic energy that their motion is influenced by the attractions between them
B. they must gain enough kinetic energy ti allow them to move freely while still being attracted to one another
C. They must lose enough of their kinetic energy so that the attractions between them hold in place as they vibrate
D. They must gain enough kinetic energy to break out of their ridged structure and move independently

Uranium has two naturally occurring isotopes. 238u has a natural abundance of 99.3% and 235u has an abundance of 0.7%. it is the rarer 235u that is needed for nuclear reactors. the isotopes are separated by forming uranium hexafluoride uf6, which is a gas, then allowing it to diffuse through a series of porous membranes. 235uf6 has a slightly larger rms speed than 238uf6 and diffuses slightly faster. many repetitions of this procedure gradually separate the two isotopes. what is the ratio of the rms speed of 235uf6 to that of 238uf6? express your answer to five significant figures.