One way to improve insulation in windows is to fill a sealed space between two glass panes with a gas that has a lower thermal conductivity than that of air. The thermal conductivity k of a gas depends on its molar heat capacity CV, molar mass M, and molecular radius r. The dependence on those quantities at a given temperature is approximated by k∝CV/r2M−−√. The noble gases have properties that make them particularly good choices as insulating gases. Noble gases range from helium (molar mass 4.0 g/mol, molecular radius 0.13 nm) to xenon (molar mass 131 g/mol, molecular radius 0.22 nm). (The noble gas radon is heavier than xenon, but radon is radioactive and so is not suitable for this purpose.)

Estimate the ratio of the thermal conductivity of Xe to that of He
a. 0.015
b. 0.061
c. 010
d. 017