Hydrogen bonding is the term which represent an intermolecular force in a sample of water.
The water molecules forming hydrogen bond with one another. The partial negative charge on the oxygen atom of one molecule form hydrogen bond with the partial positive charge on the hydrogen of other molecules.water molecules are also attracted to other polar molecule and ions
Diffusion is the process of a substance spreading out to evenly fill its container or environment. Rate of diffusion of a gas is inversely proportional to the molar mass of the gas.

Lighter(lower) the molar mass of the gas , faster will be its rate of diffusion and heavier (higher) the molar mass of the gas , slower will be its rate of diffusion.
We have to arrange the given gases from slowest rate of diffusion to fastest rate of diffusion that means we need to arrange gases from higher molar mass to lower molar mass.
Molar mass of given gases are :
Cl = 35.5 g/mol
Xe = 131.29 g/mol
He = 4.00 g/mol
N = 14.00 g/mol
So correct order for slowest rate of diffusion (highest molar mass) to fastest rate of diffusion (lowest molar mass) is :
Xe , Cl , N , He
Xe having the highest molar mass will have the slowest rate of diffusion and He with lowest molar mass will have the fastest rate of diffusion, so option 'c' is correct.
Note : Slowest rate of diffusion = High Molar Mass
Fastest rate of diffusion = Low Molar Mass
M(H₂O) = 97,2 g.
n(H₂O) = m(H₂O) ÷ M(H₂O).
n(H₂O) = 97,2 g ÷ 18 g/mol.
n(H₂O) = 5,4 mol.
N(H₂O) = n(H₂O) · Na.
N(H₂O) = 5,4 mol · 6,023·10²³ 1/mol.
N(H₂O) = 3,25·10²⁴ molecules of water.
n - amount of substance.
Na - Avogadro number.
Answer: The Sun Could Be Seen Once during the year when north of the equator.