<u>Answer:</u> The de-Broglie's wavelength of a hydrogen molecule is 
<u>Explanation:</u>
Kinetic energy is the measure of temperature of the system.
The equation used to calculate kinetic energy of a particle follows:

where,
E = kinetic energy of the particles = ?
k = Boltzmann constant = 
T = temperature of the particle = 30 K
Putting values in above equation, we get:

- Calculating the mass of 1 molecule of hydrogen gas:
Conversion factor used: 1 kg = 1000 g
1 mole of hydrogen gas has a mass of 2 grams or
According to mole concept:
number of molecules occupy 1 mole of a gas.
As,
number of hydrogen molecules has a mass of 
So, 1 molecule of hydrogen will have a mass of = 
- To calculate the wavelength of a particle, we use the equation given by De-Broglie's wavelength, which is:

where,
= De-Broglie's wavelength = ?
h = Planck's constant = 
m = mass of 1 hydrogen molecule = 
= kinetic energy of the particle = 
Putting values in above equation, we get:

(Conversion factor:
)
Hence, the de-Broglie's wavelength of a hydrogen molecule is 