I believe it is the second option
Answer:
20 km
Explanation:
he walks 10 km + another 10 km so 20 :)
Helium gas would be the one to effuse faster as compared to krypton. This is because krypton is heavier than helium. Heavier molecules would require more energy to move so they tend to effuse slower than molecules that are lighter which will only require less energy.
