Answer: Option (a) is the correct answer.
Step-by-step explanation:
According to Graham's law, rate of diffusion or effusion is inversely proportional to the square root of molecular weight.
Mathematically, Rate of diffusion or effusion =

where M = mass or molecular weight of gas
Therefore, in the given options, mass of the gases is as follows.
Nitrogen = 14.00 g/mol
Neon = 20.17 g/mol
Argon = 39.94 g/mol
Krypton = 83.79 g/mol
Hence, more is the mass of gas less will be its rate of diffusion. Thus, we can conclude that correct order from slowest to fastest will be as follows.
Kr < Ar < Ne < N