Why does Avogadro's principle hold true for gases that have large particles and also for gases that have small particles?
the kinetic energy of a large particle and a small particle are the same at the same temperature
A large particle is like a mack truck it may not move very fast because of its mass and inertia but it makes up for the lack of velocity with its heavy mass
A small particle is like a sports care it may not have much for mass but it has a very fast velocity. The velocity squared makes up for the small mass.
temperature is a measure of kinetic energy so all particles regardless of their size have the same kinetic energy at the same temperature.