enmoles of helium gas and one mole of solid argon are in thermal equilibrium with each other at 10 K. Both helium and argon are monatomic, and argon is ten times as massive as helium. How do the average speeds of the atoms in these two substances compare under the conditions specified

Average speed of helium is higher than argon.

Explanation:

The average speed of helium is higher than argon atom under the conditions specified because of lower mass of the helium atom as compared to argon atom. Average speed of an atom is inversely proportional to mass of the atom. If mass of an atom decreases, the atom moves with higher speed while on the other hand, if the mass of an atom increases the average speed of an atom decreases.