The ratio of de-Broglie wavelengths of molecules of hydrogen and helium which are at temperature 27 degree C and 127 degree C respectively its
(d) 3/5 (All options are under square root)
de Broglie wavelength, λ = h/(2πmkT)
where h - Planck's constant, m - mass of atom, k - Boltzmann constant, T - temperature in K.
Hydrogen molecules, H2, will have 2 protons,
Helium molecules will have 2 protons and 2 neutrons. Masses of protons and neutrons are approximately same. Hence Helium gas molecule will be TWICE massive than hydrogen molecule.
λHydrogen/λHelium = [(mT)Hydrogen/(mT)Helium] = (300/(2x400)) = (3/8)