Uranium Has Two Isotopes U²³⁸ and U²³⁵

Uranium has two isotopes U²³⁸ and U²³⁵.Enriched uranium,with a greater fraction of U²³⁵ required by nuclear reactors,is synthesized by first forming the compound UF₆ in the gaseous form and then allowing it to pass through a porous medium.The two isotopes are then separated by diffusion which depends on the rms speeds of the molecules.Given the mass of a fluorine atom is 19 amu,masses of U²³⁵ and U²³⁸ atoms are 235.043924 amu and 238.050785 amu,respectively,the ratio of the rms speeds of the two uranium hexafluoride molecules is

A) 1.1000.
B) 1.0043.
C) 1.0420.
D) 1.0680.
E) 10.459.